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by Chris Woodford . Last updated: November 22, 2022.

Photo: Air pollution is obvious when it pours from a smokestack (chimney), but it's not always so easy to spot. This is an old photo of the kind of smoke that used to come from coal-fired power plants and, apart from soot (unburned carbon particles), its pollutants include sulfur dioxide and the greenhouse gas carbon dioxide. Thanks to tougher pollution controls, modern power plants produce only a fraction as much pollution. Modern pollution made by traffic consists of gases like nitrogen dioxide and "particulates" (microscopic soot and dust fragments) that are largely invisible.

What is air pollution?

Air pollution is a gas (or a liquid or solid dispersed through ordinary air) released in a big enough quantity to harm the health of people or other animals, kill plants or stop them growing properly, damage or disrupt some other aspect of the environment (such as making buildings crumble), or cause some other kind of nuisance (reduced visibility, perhaps, or an unpleasant odor).

Natural air pollution

Photo: Forest fires are a completely natural cause of air pollution. We'll never be able to prevent them breaking out or stop the pollution they cause; our best hope is to manage forests, where we can, so fires don't spread. Ironically, that can mean deliberately burning areas of forest, as shown here, to create firebreaks. Forests are also deliberately burned to regenerate ecosystems. Photo by courtesy of US Fish and Wildlife Service .

Top-ten kinds of air pollution Photo: Flying molecules—if you could see air pollution close up, this is what it would look like. Image courtesy of US Department of Energy. Any gas could qualify as pollution if it reached a high enough concentration to do harm. Theoretically, that means there are dozens of different pollution gases. It's important to note that not all the things we think of as pollution are gases: some are aerosols (liquids or solids dispersed through gases). In practice, about ten different substances cause most concern: Sulfur dioxide : Coal, petroleum, and other fuels are often impure and contain sulfur as well as organic (carbon-based) compounds. When sulfur (spelled "sulphur" in some countries) burns with oxygen from the air, sulfur dioxide (SO 2 ) is produced. Coal-fired power plants are the world's biggest source of sulfur-dioxide air pollution, which contributes to smog, acid rain, and health problems that include lung disease. [5] Large amounts of sulfur dioxide are also produced by ships, which use dirtier diesel fuel than cars and trucks. [6] Carbon monoxide : This highly dangerous gas forms when fuels have too little oxygen to burn completely. It spews out in car exhausts and it can also build up to dangerous levels inside your home if you have a poorly maintained gas boiler , stove, or fuel-burning appliance. (Always fit a carbon monoxide detector if you burn fuels indoors.) [7] Carbon dioxide : This gas is central to everyday life and isn't normally considered a pollutant: we all produce it when we breathe out and plants such as crops and trees need to "breathe" it in to grow. However, carbon dioxide is also a greenhouse gas released by engines and power plants. Since the beginning of the Industrial Revolution, it's been building up in Earth's atmosphere and contributing to the problem of global warming and climate change . [8] Nitrogen oxides : Nitrogen dioxide (NO 2 ) and nitrogen oxide (NO) are pollutants produced as an indirect result of combustion, when nitrogen and oxygen from the air react together. Nitrogen oxide pollution comes from vehicle engines and power plants, and plays an important role in the formation of acid rain, ozone and smog. Nitrogen oxides are also "indirect greenhouse gases" (they contribute to global warming by producing ozone, which is a greenhouse gas). [9] Volatile organic compounds (VOCs) : These carbon-based (organic) chemicals evaporate easily at ordinary temperatures and pressures, so they readily become gases. That's precisely why they're used as solvents in many different household chemicals such as paints , waxes, and varnishes. Unfortunately, they're also a form of air pollution: they're believed to have long-term (chronic) effects on people's health and they play a role in the formation of ozone and smog. VOCs are also released by tobacco smoke and wildfires. [10] Particulates : There are many different kinds of particulates, from black soot in diesel exhaust to dust and organic matter from the desert. Airborne liquid droplets from farm pollution also count as particulates. Particulates of different sizes are often referred to by the letters PM followed by a number, so PM 10 means soot particles of less than 10 microns (10 millionths of a meter or 10µm in diameter, roughly 10 times thinner than a thick human hair). The smaller ("finer") the particulates, the deeper they travel into our lungs and the more dangerous they are. PM 2.5 particulates are much more dangerous (they're less than 2.5 millionths of a meter or about 40 times thinner than a typical hair). In cities, most particulates come from traffic fumes. [11] Ozone : Also called trioxygen, this is a type of oxygen gas whose molecules are made from three oxygen atoms joined together (so it has the chemical formula O 3 ), instead of just the two atoms in conventional oxygen (O 2 ). In the stratosphere (upper atmosphere), a band of ozone ("the ozone layer") protects us by screening out harmful ultraviolet radiation (high-energy blue light) beaming down from the Sun. At ground level, it's a toxic pollutant that can damage health. It forms when sunlight strikes a cocktail of other pollution and is a key ingredient of smog (see box below). [12] Chlorofluorocarbons (CFCs) : Once thought to be harmless, these gases were widely used in refrigerators and aerosol cans until it was discovered that they damaged Earth's ozone layer. We discuss this in more detail down below. [13] Unburned hydrocarbons : Petroleum and other fuels are made of organic compounds based on chains of carbon and hydrogen atoms. When they burn properly, they're completely converted into harmless carbon dioxide and water ; when they burn incompletely, they can release carbon monoxide or float into the air in their unburned form, contributing to smog. Lead and heavy metals : Lead and other toxic "heavy metals" can be spread into the air either as toxic compounds or as aerosols (when solids or liquids are dispersed through gases and carried through the air by them) in such things as exhaust fumes and the fly ash (contaminated waste dust) from incinerator smokestacks. [14] What are the causes of air pollution?

Photo: Even in the age of electric cars, traffic remains a major cause of air pollution. Photo by Warren Gretz courtesy of US DOE National Renewable Energy Laboratory (NREL) (NREL photo id#46361).

Photo: Brown smog lingers over Denver, Colorado. Photo by Warren Gretz courtesy of US DOE National Renewable Energy Laboratory (NREL) (NREL photo id#56919).

Chart: Most of the world's major cities routinely exceed World Health Organization (WHO) air pollution guidelines, though progress is being made: you can see that the 2022 figures (green) show a marked improvement on the 2016 ones (orange) in almost every case. This chart compares annual mean PM 2.5 levels in 12 representative cities around the world with the recently revised (2021) WHO guideline value of 5μg per cubic meter (dotted line). PM 2.5 particulates are those smaller than 2.5 microns and believed to be most closely linked with adverse health effects. For more about this chart and the data sources used, see note [22] .

Photo: Smokestacks billowing pollution over Moscow, Russia in 1994. Factory pollution is much less of a problem than it used to be in the world's "richer" countries—partly because a lot of their industry has been exported to nations such as China, India, and Mexico. Photo by Roger Taylor courtesy of US DOE National Renewable Energy Laboratory (NREL) .

What effects does air pollution have?

Photo: Air pollution can cause a variety of lung diseases and other respiratory problems. This chest X ray shows a lung disease called emphysema in the patient's left lung. A variety of things can cause it, including smoking and exposure to air pollution. Photo courtesy of National Heart, Lung and Blood Institute (NHLBI) and National Institutes of Health.

" In 2016, 91% of the world population was living in places where the WHO air quality guidelines levels were not met." World Health Organization , 2018

Photo: For many years, the stonework on the Parthenon in Athens, Greece has been blackened by particulates from traffic pollution, but other sources of pollution, such as wood-burning stoves, are increasingly significant. Photo by Michael M. Reddy courtesy of U.S. Geological Survey .

How air pollution works on different scales

Indoor air pollution.

Photo: Air freshener—or air polluter?

Further reading

Acid rain—a closer look.

Photo: Acid rain can turn lakes so acidic that fish no longer survive. Picture courtesy of U.S. Fish and Wildlife Service Division of Public Affairs. Why does that matter? Pure water is neither acidic nor alkaline but completely neutral (we say it has an acidity level or pH of 7.0). Ordinary rainwater is a little bit more acidic than this with about the same acidity as bananas (roughly pH 5.5), but if rain falls through sulfur dioxide pollution it can turn much more acidic (with a pH of 4.5 or lower, which is the same acidity as orange or lemon juice). When acid rain accumulates in lakes or rivers, it gradually turns the entire water more acidic. That's a real problem because fish thrive only in water that is neutral or slightly acidic (typically with a pH of 6.5–7.0). Once the acidity drops below about pH 6.0, fish soon start to die—and if the pH drops to about 4.0 or less, all the fish will be killed. Acid rain has caused major problems in lakes throughout North America and Europe. It also causes the death of forests, reduces the fertility of soil, and damages buildings by eating away stonework (the marble on the US Capitol in Washington, DC has been eroded by acid-rain, for example). One of the biggest difficulties in tackling acid rain is that it can happen over very long distances. In one notable case, sulfur dioxide air pollution produced by power plants in the UK was blamed for causing acid rain that fell on Scandinavian countries such as Norway, producing widespread damage to forests and the deaths of thousands of fish in acidified lakes. The British government refused to acknowledge the problem and that was partly why the UK became known as the "dirty man of Europe" in the 1980s and 1990s. [18] Acid rain was a particular problem in the last 30–40 years of the 20th century. Thanks to the decline in coal-fired power plants, and the sulfur dioxide they spewed out, it's less of a problem for western countries today. But it's still a big issue in places like India, where coal remains a major source of energy. Global air pollution It's hard to imagine doing anything so dramatic and serious that it would damage our entire, enormous planet—but, remarkable though it may seem, we all do things like this everyday, contributing to problems such as global warming and the damage to the ozone layer (two separate issues that are often confused). Global warming Every time you ride in a car, turn on the lights, switch on your TV , take a shower, microwave a meal, or use energy that's come from burning a fossil fuel such as oil, coal, or natural gas, you're almost certainly adding to the problem of global warming and climate change: unless it's been produced in some environmentally friendly way, the energy you're using has most likely released carbon dioxide gas into the air. While it's not an obvious pollutant, carbon dioxide has gradually built up in the atmosphere, along with other chemicals known as greenhouse gases . Together, these gases act a bit like a blanket surrounding our planet that is slowly making the mean global temperature rise, causing the climate (the long-term pattern of our weather) to change, and producing a variety of different effects on the natural world, including rising sea levels. Read more in our main article about global warming and climate change . Ozone holes

How can we solve the problem of air pollution?

Photo: Pollution solution: an electrostatic smoke precipitator helps to prevent air pollution from this smokestack at the McNeil biomass power plant in Burlington, VT. Photo by Warren Gretz courtesy of US DOE National Renewable Energy Laboratory (NREL).

What can you do to help reduce air pollution?

Photo: Buying organic food reduces the use of sprayed pesticides and other chemicals, so it helps to reduce air (as well as water) pollution.

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• Climate change and global warming
• Environmentalism (introduction)
• Land pollution
• Organic food and farming
• Renewable energy
• Water pollution

• Breathless: Why Air Pollution Matters—and How it Affects You by Chris Woodford. Icon, 2021. My new book explores the problem in much more depth than I've been able to go into here. You can also read a bonus chapter called Angels with dirty faces: How air pollution blackens our buildings and monuments .
• The Invisible Killer: The Rising Global Threat of Air Pollution and How We Can Fight Back by Gary Fuller. Melville House, 2018.
• Reducing Pollution and Waste by Jen Green. Raintree/Capstone, 2011. A 48-page introduction for ages 9–12. The emphasis here is on getting children to think about pollution: where it comes from, who makes it, and who should solve the problem.
• Pollution Crisis by Russ Parker. Rosen, 2009. A 32-page guide for ages 8–10. It starts with a global survey of the problem; looks at air, water, and land pollution; then considers how we all need to be part of the solution.
• Earth Matters by Lynn Dicks et al. Dorling Kindersley, 2008. This isn't specifically about pollution. Instead, it explores how a range of different environmental problems are testing life to the limit in the planet's major biomes (oceans, forests, and so on). I wrote the section of this book that covers the polar regions.
• State of Global Air : One of the best sources of global air pollution data.
• American Lung Association: State of the Air Report : A good source of data about the United States.
• European Environment Agency: Air quality in Europe : A definitive overview of the situation in the European countries.
• World Health Organization (WHO) Ambient (outdoor) air pollution in cities database : A spreadsheet of pollution data for most major cities in the world (a little out of date, but a new version is expected soon).
• Our World in Data : Accessible guides to global data from Oxford University.
• The New York Times Topics: Air Pollution
• The Guardian: Pollution
• Wired: Pollution
• 'Invisible killer': fossil fuels caused 8.7m deaths globally in 2018, research finds by Oliver Milman. The Guardian, February 9, 2021. Pollution of various kinds causes something like one in five of all deaths.
• Millions of masks distributed to students in 'gas chamber' Delhi : BBC News, 1 November 2019.
• 90% of world's children are breathing toxic air, WHO study finds by Matthew Taylor. The Guardian, October 29, 2018. The air pollution affecting billions of children could continue to harm their health throughout their lives.
• Pollution May Dim Thinking Skills, Study in China Suggests by Mike Ives. The New York Times, August 29, 2018. Long-term exposure to air pollution seems to cause a decline in cognitive skills.
• Global pollution kills 9m a year and threatens 'survival of human societies' by Damian Carrington. The Guardian, October 19, 2017. Air, water, and land pollution kill millions, cost trillions, and threaten the very survival of humankind, a new study reveals.
• India's Air Pollution Rivals China's as World's Deadliest by Geeta Anand. The New York Times, February 14, 2017. High levels of pollution could be killing 1.1 million Indians each year.
• More Than 9 in 10 People Breathe Bad Air, WHO Study Says by Mike Ives. The New York Times, September 27, 2016. New WHO figures suggest the vast majority of us are compromising our health by breathing bad air.
• Study Links 6.5 Million Deaths Each Year to Air Pollution by Stanley Reed. The New York Times, June 26, 2016. Air pollution deaths are far greater than previously supposed according to a new study by the International Energy Agency.
• UK air pollution 'linked to 40,000 early deaths a year' by Michelle Roberts, BBC News, February 23, 2016. Diesel engines, cigarette smoke, and even air fresheners are among the causes of premature death from air pollution.
• This Wearable Detects Pollution to Build Air Quality Maps in Real Time by Davey Alba. Wired, November 19, 2014. A wearable pollution gadget lets people track their exposure to air pollution through a smartphone app.
• Air pollution and public health: emerging hazards and improved understanding of risk by Frank J. Kelly and Julia C. Fussell, Environmental Geochemistry and Health, 2015
• Health effects of fine particulate air pollution: lines that connect by C.A. Pope and D.W. Dockery. Journal of the Air and Waste Management Association, 2006
• Ambient and household air pollution: complex triggers of disease by Stephen A. Farmer et al, Am J Physiol Heart Circ Physiol, 2014

Text copyright © Chris Woodford 2010, 2022. All rights reserved. Full copyright notice and terms of use .

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Air Pollution

Our overview of indoor and outdoor air pollution.

By: Hannah Ritchie and Max Roser

This article was first published in October 2017 and last revised in February 2024.

Air pollution is one of the world's largest health and environmental problems. It develops in two contexts: indoor (household) air pollution and outdoor air pollution.

In this topic page, we look at the aggregate picture of air pollution – both indoor and outdoor. We also have dedicated topic pages that look in more depth at these subjects:

Indoor Air Pollution

Look in detail at the data and research on the health impacts of Indoor Air Pollution, attributed deaths, and its causes across the world

Outdoor Air Pollution

Look in detail at the data and research on exposure to Outdoor Air Pollution, its health impacts, and attributed deaths across the world

Look in detail at the data and research on energy consumption, its impacts around the world today, and how this has changed over time

See all interactive charts on Air Pollution ↓

Other research and writing on air pollution on Our World in Data:

• Air pollution: does it get worse before it gets better?
• Data Review: How many people die from air pollution?
• Energy poverty and indoor air pollution: a problem as old as humanity that we can end within our lifetime
• How many people do not have access to clean fuels for cooking?
• What are the safest and cleanest sources of energy?
• What the history of London’s air pollution can tell us about the future of today’s growing megacities
• When will countries phase out coal power?

Air pollution is one of the world's leading risk factors for death

Air pollution is responsible for millions of deaths each year.

Air pollution – the combination of outdoor and indoor particulate matter and ozone – is a risk factor for many of the leading causes of death, including heart disease, stroke, lower respiratory infections, lung cancer, diabetes, and chronic obstructive pulmonary disease (COPD).

The Institute for Health Metrics and Evaluation (IHME), in its Global Burden of Disease study, provides estimates of the number of deaths attributed to the range of risk factors for disease. 1

In the visualization, we see the number of deaths per year attributed to each risk factor. This chart shows the global total but can be explored for any country or region using the "change country" toggle.

Air pollution is one of the leading risk factors for death. In low-income countries, it is often very near the top of the list (or is the leading risk factor).

Air pollution contributes to one in ten deaths globally

In recent years, air pollution has contributed to one in ten deaths globally. 2

In the map shown here, we see the share of deaths attributed to air pollution across the world.

Air pollution is one of the leading risk factors for disease burden

Air pollution is one of the leading risk factors for death. But its impacts go even further; it is also one of the main contributors to the global disease burden.

Global disease burden takes into account not only years of life lost to early death but also the number of years lived in poor health.

In the visualization, we see risk factors ranked in order of DALYs – disability-adjusted life years – the metric used to assess disease burden. Again, air pollution is near the top of the list, making it one of the leading risk factors for poor health across the world.

Air pollution not only takes years from people's lives but also has a large effect on the quality of life while they're still living.

Who is most affected by air pollution?

Death rates from air pollution are highest in low-to-middle-income countries.

Air pollution is a health and environmental issue across all countries of the world but with large differences in severity.

In the interactive map, we show death rates from air pollution across the world, measured as the number of deaths per 100,000 people in a given country or region.

The burden of air pollution tends to be greater across both low and middle-income countries for two reasons: indoor pollution rates tend to be high in low-income countries due to a reliance on solid fuels for cooking, and outdoor air pollution tends to increase as countries industrialize and shift from low to middle incomes.

A map of the number of deaths from air pollution by country can be found here .

How are death rates from air pollution changing?

Death rates from air pollution are falling – mainly due to improvements in indoor pollution.

In the visualization, we show global death rates from air pollution over time – shown as the total air pollution – in addition to the individual contributions from outdoor and indoor pollution.

Globally, we see that in recent decades, the death rates from total air pollution have declined: since 1990, death rates have nearly halved. But, as we see from the breakdown, this decline has been primarily driven by improvements in indoor air pollution.

Death rates from indoor air pollution have seen an impressive decline, while improvements in outdoor pollution have been much more modest.

You can explore this data for any country or region using the "change country" toggle on the interactive chart.

Interactive charts on air pollution

Murray, C. J., Aravkin, A. Y., Zheng, P., Abbafati, C., Abbas, K. M., Abbasi-Kangevari, M., ... & Borzouei, S. (2020). Global burden of 87 risk factors in 204 countries and territories, 1990–2019: a systematic analysis for the Global Burden of Disease Study 2019 .  The Lancet ,  396 (10258), 1223-1249.

Here, we use the term 'contributes,' meaning it was one of the attributed risk factors for a given disease or cause of death. There can be multiple risk factors for a given disease that can amplify one another. This means that in some cases, air pollution was not the only risk factor but one of several.

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ENCYCLOPEDIC ENTRY

Air pollution.

Air pollution consists of chemicals or particles in the air that can harm the health of humans, animals, and plants. It also damages buildings.

Biology, Ecology, Earth Science, Geography

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Air pollution consists of chemicals or particles in the air that can harm the health of humans, animals, and plants. It also damages buildings. Pollutants in the air take many forms. They can be gases , solid particles, or liquid droplets. Sources of Air Pollution Pollution enters the Earth's atmosphere in many different ways. Most air pollution is created by people, taking the form of emissions from factories, cars, planes, or aerosol cans . Second-hand cigarette smoke is also considered air pollution. These man-made sources of pollution are called anthropogenic sources . Some types of air pollution, such as smoke from wildfires or ash from volcanoes , occur naturally. These are called natural sources . Air pollution is most common in large cities where emissions from many different sources are concentrated . Sometimes, mountains or tall buildings prevent air pollution from spreading out. This air pollution often appears as a cloud making the air murky. It is called smog . The word "smog" comes from combining the words "smoke" and " fog ." Large cities in poor and developing nations tend to have more air pollution than cities in developed nations. According to the World Health Organization (WHO) , some of the worlds most polluted cities are Karachi, Pakistan; New Delhi, India; Beijing, China; Lima, Peru; and Cairo, Egypt. However, many developed nations also have air pollution problems. Los Angeles, California, is nicknamed Smog City. Indoor Air Pollution Air pollution is usually thought of as smoke from large factories or exhaust from vehicles. But there are many types of indoor air pollution as well. Heating a house by burning substances such as kerosene , wood, and coal can contaminate the air inside the house. Ash and smoke make breathing difficult, and they can stick to walls, food, and clothing. Naturally-occurring radon gas, a cancer -causing material, can also build up in homes. Radon is released through the surface of the Earth. Inexpensive systems installed by professionals can reduce radon levels. Some construction materials, including insulation , are also dangerous to people's health. In addition, ventilation , or air movement, in homes and rooms can lead to the spread of toxic mold . A single colony of mold may exist in a damp, cool place in a house, such as between walls. The mold's spores enter the air and spread throughout the house. People can become sick from breathing in the spores. Effects On Humans People experience a wide range of health effects from being exposed to air pollution. Effects can be broken down into short-term effects and long-term effects . Short-term effects, which are temporary , include illnesses such as pneumonia or bronchitis . They also include discomfort such as irritation to the nose, throat, eyes, or skin. Air pollution can also cause headaches, dizziness, and nausea . Bad smells made by factories, garbage , or sewer systems are considered air pollution, too. These odors are less serious but still unpleasant . Long-term effects of air pollution can last for years or for an entire lifetime. They can even lead to a person's death. Long-term health effects from air pollution include heart disease , lung cancer, and respiratory diseases such as emphysema . Air pollution can also cause long-term damage to people's nerves , brain, kidneys , liver , and other organs. Some scientists suspect air pollutants cause birth defects . Nearly 2.5 million people die worldwide each year from the effects of outdoor or indoor air pollution. People react differently to different types of air pollution. Young children and older adults, whose immune systems tend to be weaker, are often more sensitive to pollution. Conditions such as asthma , heart disease, and lung disease can be made worse by exposure to air pollution. The length of exposure and amount and type of pollutants are also factors. Effects On The Environment Like people, animals, and plants, entire ecosystems can suffer effects from air pollution. Haze , like smog, is a visible type of air pollution that obscures shapes and colors. Hazy air pollution can even muffle sounds. Air pollution particles eventually fall back to Earth. Air pollution can directly contaminate the surface of bodies of water and soil . This can kill crops or reduce their yield . It can kill young trees and other plants. Sulfur dioxide and nitrogen oxide particles in the air, can create acid rain when they mix with water and oxygen in the atmosphere. These air pollutants come mostly from coal-fired power plants and motor vehicles . When acid rain falls to Earth, it damages plants by changing soil composition ; degrades water quality in rivers, lakes and streams; damages crops; and can cause buildings and monuments to decay . Like humans, animals can suffer health effects from exposure to air pollution. Birth defects, diseases, and lower reproductive rates have all been attributed to air pollution. Global Warming Global warming is an environmental phenomenon caused by natural and anthropogenic air pollution. It refers to rising air and ocean temperatures around the world. This temperature rise is at least partially caused by an increase in the amount of greenhouse gases in the atmosphere. Greenhouse gases trap heat energy in the Earths atmosphere. (Usually, more of Earths heat escapes into space.) Carbon dioxide is a greenhouse gas that has had the biggest effect on global warming. Carbon dioxide is emitted into the atmosphere by burning fossil fuels (coal, gasoline , and natural gas ). Humans have come to rely on fossil fuels to power cars and planes, heat homes, and run factories. Doing these things pollutes the air with carbon dioxide. Other greenhouse gases emitted by natural and artificial sources also include methane , nitrous oxide , and fluorinated gases. Methane is a major emission from coal plants and agricultural processes. Nitrous oxide is a common emission from industrial factories, agriculture, and the burning of fossil fuels in cars. Fluorinated gases, such as hydrofluorocarbons , are emitted by industry. Fluorinated gases are often used instead of gases such as chlorofluorocarbons (CFCs). CFCs have been outlawed in many places because they deplete the ozone layer . Worldwide, many countries have taken steps to reduce or limit greenhouse gas emissions to combat global warming. The Kyoto Protocol , first adopted in Kyoto, Japan, in 1997, is an agreement between 183 countries that they will work to reduce their carbon dioxide emissions. The United States has not signed that treaty . Regulation In addition to the international Kyoto Protocol, most developed nations have adopted laws to regulate emissions and reduce air pollution. In the United States, debate is under way about a system called cap and trade to limit emissions. This system would cap, or place a limit, on the amount of pollution a company is allowed. Companies that exceeded their cap would have to pay. Companies that polluted less than their cap could trade or sell their remaining pollution allowance to other companies. Cap and trade would essentially pay companies to limit pollution. In 2006 the World Health Organization issued new Air Quality Guidelines. The WHOs guidelines are tougher than most individual countries existing guidelines. The WHO guidelines aim to reduce air pollution-related deaths by 15 percent a year. Reduction Anybody can take steps to reduce air pollution. Millions of people every day make simple changes in their lives to do this. Taking public transportation instead of driving a car, or riding a bike instead of traveling in carbon dioxide-emitting vehicles are a couple of ways to reduce air pollution. Avoiding aerosol cans, recycling yard trimmings instead of burning them, and not smoking cigarettes are others.

Downwinders The United States conducted tests of nuclear weapons at the Nevada Test Site in southern Nevada in the 1950s. These tests sent invisible radioactive particles into the atmosphere. These air pollution particles traveled with wind currents, eventually falling to Earth, sometimes hundreds of miles away in states including Idaho, Utah, Arizona, and Washington. These areas were considered to be "downwind" from the Nevada Test Site. Decades later, people living in those downwind areascalled "downwinders"began developing cancer at above-normal rates. In 1990, the U.S. government passed the Radiation Exposure Compensation Act. This law entitles some downwinders to payments of $50,000.

Greenhouse Gases There are five major greenhouse gases in Earth's atmosphere.

• water vapor
• carbon dioxide
• nitrous oxide

London Smog What has come to be known as the London Smog of 1952, or the Great Smog of 1952, was a four-day incident that sickened 100,000 people and caused as many as 12,000 deaths. Very cold weather in December 1952 led residents of London, England, to burn more coal to keep warm. Smoke and other pollutants became trapped by a thick fog that settled over the city. The polluted fog became so thick that people could only see a few meters in front of them.

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Related Resources

What You Need to Know About Climate Change and Air Pollution

#ShowYourStripes graphic by Professor Ed Hawkins (University of Reading) https://showyourstripes.info/

How big a problem is air pollution globally?

Air pollution is the world’s leading environmental cause of illness and premature death. Fine air pollution particles or aerosols, also known as fine particulate matter or PM 2.5 , are responsible for 6.4 million deaths every year, caused by diseases such as ischemic heart disease, stroke, lung cancer, chronic obstructive pulmonary disease, pneumonia, type 2 diabetes, and neonatal disorders. About 95% of these deaths occur in developing countries, where billions of people are exposed to outdoor and indoor concentrations of PM 2.5 that are multiple times higher than guidelines established by the World Health Organization. A World Bank report estimated that the cost of the health damage caused by air pollution amounts to $8.1 trillion a year, equivalent to 6.1% of global GDP.

Poor people, elderly people, and young children who come from poor families are the most affected and the least likely to be able to cope with the health impacts that come with air pollution. Global health crises such as the COVID-19 pandemic weaken the resilience of societies. Compounding this, exposure to air pollution is linked to increased incidence of COVID-19-related hospital admissions and mortality. In addition to health, air pollution is also linked to biodiversity and ecosystem loss , and has adverse impacts on human capital . Reducing air pollution, on the other hand, not only improves health but strengthens economies. A recent World Bank study found that a 20% decrease in PM 2.5 concentration is associated with a 16% increase in employment growth rate and a 33% increase in labor productivity growth rate .

A World Bank report estimated that the cost of the health damage caused by air pollution amounts to $8.1 trillion a year, equivalent to 6.1% of global GDP.

How is air pollution related to climate change?

Air pollution and climate change are two sides of the same coin, but they are typically addressed separately. They should be tackled jointly, with a focus on protecting peoples’ health – particularly in low- and middle-income countries – to strengthen human capital and reduce poverty.

Air pollutants and greenhouse gases often come from the same sources, such as coal-fired power plants and diesel-fueled vehicles. Some air pollutants do not last long in the environment, notably black carbon – a part of fine particulate matter (PM 2.5 ). Other short-lived climate pollutants (SLCPs) include methane, hydrofluorocarbons, and ground-level or tropospheric ozone. SLCPs are far more potent climate warmers than carbon dioxide. Methane is a precursor of ground-level ozone, which according to the Climate and Clean air Coalition and Stockholm Environment Institute, kills about a million people each year, and is 80 times more potent at warming the planet than carbon dioxide over a 20-year period. Their relatively short lifespans, coupled with their strong warming potential, means that interventions to reduce SLCP emissions can deliver climate benefits in a relatively short time. If we address short-lived climate pollutants, we gain dual benefits: better air quality and improved health where we live, and the global benefit of mitigating climate change.

A World Bank study found that PM 2.5 from the burning of fossil fuels such as coal combustion or diesel-fueled vehicle emissions is among the most toxic types of PM 2.5 . Particles from these sources are more damaging to health than particles from most other air pollution sources. Addressing these sources of PM 2.5 -- like coal combustion and traffic – would address the most toxic air pollution. Given that these sources are also key contributors to climate warming, tackling air pollution from these sources also mitigates climate change.  

What are some requirements for effectively addressing air pollution?

Measure it and monitor it . Many developing countries do not have even rudimentary infrastructure for measuring air pollution. A World Bank study found that there was only one PM 2.5 ground-level monitor per 65 million people in low-income countries , and one per 28 million people in Sub-Saharan Africa;  in contrast, there is one monitor per 370,000 people in high-income countries. This is a serious issue, because you cannot properly manage what you do not measure. If you don't know how bad your problem is, you won’t know whether anything you do to fix it is effective. Countries need to establish ground-level monitoring networks and operate and maintain them properly so they yield reliable air quality data.

Know the main sources of air pollution and their contributions to poor air quality. For example, in City A, transport may be the biggest contributor, but in City B, it could be something completely different, such as emissions from dirty cooking fuels seeping from homes into the outside environment. With this information you can target interventions appropriately to abate air pollution. There are certainly intuitive, no-regret steps cities and countries can take to tackle air pollution, such as shifting to clean buses or renewable energy. But if you want to address air pollution comprehensively, you need to understand what your own sources are.

Disseminate air quality data to the public . People have a right to know the quality of the air they're breathing. Disseminating this information exerts pressure on those who can make the needed changes. Air quality data should be easily accessible in formats that are widely understood so people can reduce their exposure to air pollution and protect vulnerable groups such as young children, the elderly, and people with health conditions that can be exacerbated by poor air quality.

What are some interventions that countries can implement to reduce air pollution?

Reducing air pollution may require physical investments or it may require policy reforms or both. Not every intervention fits every context. Interventions whose benefits (notably improved health) outweigh the costs should be selected. Part of our work at the World Bank is to incorporate climate change considerations into analysis so that the climate benefits of improving air quality can be taken into account in the decision-making process. A few examples of interventions to improve air quality in different sectors:

• Energy : Change the energy mix to include cleaner, renewable energy sources and phase out subsidies that promote use of polluting fuels.
• Industry: Use renewable fuels, adopt cleaner production measures, and install scrubbers and electrostatic precipitators in industrial facilities to filter particulates from emissions before they are released into the air.
• Transport : Change from diesel to electric vehicles, install catalytic converters in vehicles to reduce toxicity of emissions, establish vehicle inspection and maintenance programs.
• Agriculture : Discourage use of nitrogen-based fertilizers; improve nitrogen-use efficiency of agricultural soils; and improve fertilizer and manure management. Nitrogen-based fertilizers release ammonia, a precursor of secondary PM 2.5 formation. Nitrogen-based fertilizers can also be oxidized and emitted to the air as nitrous oxide, a long-lived greenhouse gas.
• Cooking and heating : Promote clean cooking and heating solutions including clean stoves and boilers.

Part of our work at the World Bank is to incorporate climate change considerations into analysis so that the climate benefits of improving air quality can be taken into account in the decision-making process.

What is the World Bank doing to help?

The World Bank has invested about $52 billion in addressing pollution in the past two decades. However, we need to scale this up. Some successful projects that address air pollution include:

In China , we supported a program in the Hebei region , the largest contributor to air pollution in the country. The overall result was a reduction in the concentration of PM 2.5 in the atmosphere by almost 40% between 2013 and the end of 2017. The program linked loan disbursements to tangible results. Hebei issued the most stringent industrial emission standards in the country, replaced diesel buses with electric buses, coal stoves with gas stoves, and improved the efficiency of fertilizer use in agriculture. The program also supported effective use of a continuous emission monitoring system to track and enforce compliance by all major industrial enterprises in the province. The project delivered about 5 million tons of CO2 equivalent emissions reductions per year through interventions such as the installation of new stoves in municipalities, and addition of a new clean energy bus fleet. The emissions reductions generated from the installation of 1,221,500 new stoves alone were equivalent to taking more than 860,000 passenger cars off the road each year.

In Peru , the World Bank is supporting a project to develop environmental information systems that includes expanding the country's air quality monitoring network to six new cities. The project is also developing new systems to disseminate information on environmental quality to the public.

In Egypt, we assessed the health impacts from environmental pollution, including the effects of ambient air pollution in Greater Cairo. We found that 19,200 people died prematurely and over 3 billion days were lived with illness in Egypt in 2017 as a result of PM 2.5 air pollution in Greater Cairo and inadequate water, sanitation, and hygiene in all of Egypt. This analytical work has led to a project to reduce vehicle emissions, improve the management of solid waste, and strengthen the air and climate decision-making system in Greater Cairo .

In Vietnam , we are working with the rapidly growing city of Hanoi to simultaneously combat the issues of climate change and air pollution. We are supporting the Ministry of Environment and Natural Resources to improve the Air Quality Monitoring Network and develop an understanding of emissions sources, as well as an Air Quality Management Plan for the city.

In Lao PDR , the World Bank program supported the government in establishing stringent ambient air quality standards, including a standard for annual average concentrations of PM 2. in line with the World Health Organization’s air quality guideline value at the time. The program also supported the adoption of regulated procedures for sampling and analyzing PM 2.5 and PM 10 in air, and other pollutants in water.

We need to tackle air pollution and climate change challenges jointly rather than separately with a focus on protecting peoples’ health today, particularly in developing countries.

Can we expect better air quality in the future as countries decarbonize their economies?

First, we must continue to reduce poverty and meet the needs of poor people, whether through lower energy costs, ensuring cleaner air, or other means. With these goals in mind, we need to tackle air pollution and climate change challenges jointly rather than separately with a focus on protecting peoples’ health today, particularly in developing countries. The health benefits of reducing emissions from the burning of fossil fuels can occur in the near term. However, the reduction of carbon dioxide in the atmosphere would occur over a longer timeframe. If decarbonization efforts pay attention to non-CO 2 pollutants as well, notably PM 2.5 , we cannot only expect better air quality, but also health benefits in the short term.

Blog: Supporting a Breath of Fresh Air for Lagos

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Air Pollution: Everything You Need to Know

How smog, soot, greenhouse gases, and other top air pollutants are affecting the planet—and your health.

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What is air pollution?

What causes air pollution, effects of air pollution, air pollution in the united states, air pollution and environmental justice, controlling air pollution, how to help reduce air pollution, how to protect your health.

Air pollution  refers to the release of pollutants into the air—pollutants that are detrimental to human health and the planet as a whole. According to the  World Health Organization (WHO) , each year, indoor and outdoor air pollution is responsible for nearly seven million deaths around the globe. Ninety-nine percent of human beings currently breathe air that exceeds the WHO’s guideline limits for pollutants, with those living in low- and middle-income countries suffering the most. In the United States, the  Clean Air Act , established in 1970, authorizes the U.S. Environmental Protection Agency (EPA) to safeguard public health by regulating the emissions of these harmful air pollutants.

“Most air pollution comes from energy use and production,” says  John Walke , director of the Clean Air team at NRDC. Driving a car on gasoline, heating a home with oil, running a power plant on  fracked gas : In each case, a fossil fuel is burned and harmful chemicals and gases are released into the air.

“We’ve made progress over the last 50 years in improving air quality in the United States, thanks to the Clean Air Act. But climate change will make it harder in the future to meet pollution standards, which are designed to  protect health ,” says Walke.

Air pollution is now the world’s fourth-largest risk factor for early death. According to the 2020  State of Global Air  report —which summarizes the latest scientific understanding of air pollution around the world—4.5 million deaths were linked to outdoor air pollution exposures in 2019, and another 2.2 million deaths were caused by indoor air pollution. The world’s most populous countries, China and India, continue to bear the highest burdens of disease.

“Despite improvements in reducing global average mortality rates from air pollution, this report also serves as a sobering reminder that the climate crisis threatens to worsen air pollution problems significantly,” explains  Vijay Limaye , senior scientist in NRDC’s Science Office. Smog, for instance, is intensified by increased heat, forming when the weather is warmer and there’s more ultraviolet radiation. In addition, climate change increases the production of allergenic air pollutants, including mold (thanks to damp conditions caused by extreme weather and increased flooding) and pollen (due to a longer pollen season). “Climate change–fueled droughts and dry conditions are also setting the stage for dangerous wildfires,” adds Limaye. “ Wildfire smoke can linger for days and pollute the air with particulate matter hundreds of miles downwind.”

The effects of air pollution on the human body vary, depending on the type of pollutant, the length and level of exposure, and other factors, including a person’s individual health risks and the cumulative impacts of multiple pollutants or stressors.

Smog and soot

These are the two most prevalent types of air pollution. Smog (sometimes referred to as ground-level ozone) occurs when emissions from combusting fossil fuels react with sunlight. Soot—a type of  particulate matter —is made up of tiny particles of chemicals, soil, smoke, dust, or allergens that are carried in the air. The sources of smog and soot are similar. “Both come from cars and trucks, factories, power plants, incinerators, engines, generally anything that combusts fossil fuels such as coal, gasoline, or natural gas,” Walke says.

Smog can irritate the eyes and throat and also damage the lungs, especially those of children, senior citizens, and people who work or exercise outdoors. It’s even worse for people who have asthma or allergies; these extra pollutants can intensify their symptoms and trigger asthma attacks. The tiniest airborne particles in soot are especially dangerous because they can penetrate the lungs and bloodstream and worsen bronchitis, lead to heart attacks, and even hasten death. In  2020, a report from Harvard’s T.H. Chan School of Public Health showed that COVID-19 mortality rates were higher in areas with more particulate matter pollution than in areas with even slightly less, showing a correlation between the virus’s deadliness and long-term exposure to air pollution. 

These findings also illuminate an important  environmental justice issue . Because highways and polluting facilities have historically been sited in or next to low-income neighborhoods and communities of color, the negative effects of this pollution have been  disproportionately experienced by the people who live in these communities.

Hazardous air pollutants

A number of air pollutants pose severe health risks and can sometimes be fatal, even in small amounts. Almost 200 of them are regulated by law; some of the most common are mercury,  lead , dioxins, and benzene. “These are also most often emitted during gas or coal combustion, incineration, or—in the case of benzene—found in gasoline,” Walke says. Benzene, classified as a carcinogen by the EPA, can cause eye, skin, and lung irritation in the short term and blood disorders in the long term. Dioxins, more typically found in food but also present in small amounts in the air, is another carcinogen that can affect the liver in the short term and harm the immune, nervous, and endocrine systems, as well as reproductive functions.  Mercury  attacks the central nervous system. In large amounts, lead can damage children’s brains and kidneys, and even minimal exposure can affect children’s IQ and ability to learn.

Another category of toxic compounds, polycyclic aromatic hydrocarbons (PAHs), are by-products of traffic exhaust and wildfire smoke. In large amounts, they have been linked to eye and lung irritation, blood and liver issues, and even cancer.  In one study , the children of mothers exposed to PAHs during pregnancy showed slower brain-processing speeds and more pronounced symptoms of ADHD.

Greenhouse gases

While these climate pollutants don’t have the direct or immediate impacts on the human body associated with other air pollutants, like smog or hazardous chemicals, they are still harmful to our health. By trapping the earth’s heat in the atmosphere, greenhouse gases lead to warmer temperatures, which in turn lead to the hallmarks of climate change: rising sea levels, more extreme weather, heat-related deaths, and the increased transmission of infectious diseases. In 2021, carbon dioxide accounted for roughly 79 percent of the country’s total greenhouse gas emissions, and methane made up more than 11 percent. “Carbon dioxide comes from combusting fossil fuels, and methane comes from natural and industrial sources, including large amounts that are released during oil and gas drilling,” Walke says. “We emit far larger amounts of carbon dioxide, but methane is significantly more potent, so it’s also very destructive.” 

Another class of greenhouse gases,  hydrofluorocarbons (HFCs) , are thousands of times more powerful than carbon dioxide in their ability to trap heat. In October 2016, more than 140 countries signed the Kigali Agreement to reduce the use of these chemicals—which are found in air conditioners and refrigerators—and develop greener alternatives over time. (The United States officially signed onto the  Kigali Agreement in 2022.)

Pollen and mold

Mold and allergens from trees, weeds, and grass are also carried in the air, are exacerbated by climate change, and can be hazardous to health. Though they aren’t regulated, they can be considered a form of air pollution. “When homes, schools, or businesses get water damage, mold can grow and produce allergenic airborne pollutants,” says Kim Knowlton, professor of environmental health sciences at Columbia University and a former NRDC scientist. “ Mold exposure can precipitate asthma attacks  or an allergic response, and some molds can even produce toxins that would be dangerous for anyone to inhale.”

Pollen allergies are worsening  because of climate change . “Lab and field studies are showing that pollen-producing plants—especially ragweed—grow larger and produce more pollen when you increase the amount of carbon dioxide that they grow in,” Knowlton says. “Climate change also extends the pollen production season, and some studies are beginning to suggest that ragweed pollen itself might be becoming a more potent allergen.” If so, more people will suffer runny noses, fevers, itchy eyes, and other symptoms. “And for people with allergies and asthma, pollen peaks can precipitate asthma attacks, which are far more serious and can be life-threatening.”

More than one in three U.S. residents—120 million people—live in counties with unhealthy levels of air pollution, according to the  2023  State of the Air  report by the American Lung Association (ALA). Since the annual report was first published, in 2000, its findings have shown how the Clean Air Act has been able to reduce harmful emissions from transportation, power plants, and manufacturing.

Recent findings, however, reflect how climate change–fueled wildfires and extreme heat are adding to the challenges of protecting public health. The latest report—which focuses on ozone, year-round particle pollution, and short-term particle pollution—also finds that people of color are 61 percent more likely than white people to live in a county with a failing grade in at least one of those categories, and three times more likely to live in a county that fails in all three.

In rankings for each of the three pollution categories covered by the ALA report, California cities occupy the top three slots (i.e., were highest in pollution), despite progress that the Golden State has made in reducing air pollution emissions in the past half century. At the other end of the spectrum, these cities consistently rank among the country’s best for air quality: Burlington, Vermont; Honolulu; and Wilmington, North Carolina. 

No one wants to live next door to an incinerator, oil refinery, port, toxic waste dump, or other polluting site. Yet millions of people around the world do, and this puts them at a much higher risk for respiratory disease, cardiovascular disease, neurological damage, cancer, and death. In the United States, people of color are 1.5 times more likely than whites to live in areas with poor air quality, according to the ALA.

Historically, racist zoning policies and discriminatory lending practices known as  redlining  have combined to keep polluting industries and car-choked highways away from white neighborhoods and have turned communities of color—especially low-income and working-class communities of color—into sacrifice zones, where residents are forced to breathe dirty air and suffer the many health problems associated with it. In addition to the increased health risks that come from living in such places, the polluted air can economically harm residents in the form of missed workdays and higher medical costs.

Environmental racism isn't limited to cities and industrial areas. Outdoor laborers, including the estimated three million migrant and seasonal farmworkers in the United States, are among the most vulnerable to air pollution—and they’re also among the least equipped, politically, to pressure employers and lawmakers to affirm their right to breathe clean air.

Recently,  cumulative impact mapping , which uses data on environmental conditions and demographics, has been able to show how some communities are overburdened with layers of issues, like high levels of poverty, unemployment, and pollution. Tools like the  Environmental Justice Screening Method  and the EPA’s  EJScreen  provide evidence of what many environmental justice communities have been explaining for decades: that we need land use and public health reforms to ensure that vulnerable areas are not overburdened and that the people who need resources the most are receiving them.

In the United States, the  Clean Air Act  has been a crucial tool for reducing air pollution since its passage in 1970, although fossil fuel interests aided by industry-friendly lawmakers have frequently attempted to  weaken its many protections. Ensuring that this bedrock environmental law remains intact and properly enforced will always be key to maintaining and improving our air quality.

But the best, most effective way to control air pollution is to speed up our transition to cleaner fuels and industrial processes. By switching over to renewable energy sources (such as wind and solar power), maximizing fuel efficiency in our vehicles, and replacing more and more of our gasoline-powered cars and trucks with electric versions, we'll be limiting air pollution at its source while also curbing the global warming that heightens so many of its worst health impacts.

And what about the economic costs of controlling air pollution? According to a report on the Clean Air Act commissioned by NRDC, the annual  benefits of cleaner air  are up to 32 times greater than the cost of clean air regulations. Those benefits include up to 370,000 avoided premature deaths, 189,000 fewer hospital admissions for cardiac and respiratory illnesses, and net economic benefits of up to $3.8 trillion for the U.S. economy every year.

“The less gasoline we burn, the better we’re doing to reduce air pollution and the harmful effects of climate change,” Walke explains. “Make good choices about transportation. When you can, ride a bike, walk, or take public transportation. For driving, choose a car that gets better miles per gallon of gas or  buy an electric car .” You can also investigate your power provider options—you may be able to request that your electricity be supplied by wind or solar. Buying your food locally cuts down on the fossil fuels burned in trucking or flying food in from across the world. And most important: “Support leaders who push for clean air and water and responsible steps on climate change,” Walke says.

• “When you see in the news or hear on the weather report that pollution levels are high, it may be useful to limit the time when children go outside or you go for a jog,” Walke says. Generally, ozone levels tend to be lower in the morning.
• If you exercise outside, stay as far as you can from heavily trafficked roads. Then shower and wash your clothes to remove fine particles.
• The air may look clear, but that doesn’t mean it’s pollution free. Utilize tools like the EPA’s air pollution monitor,  AirNow , to get the latest conditions. If the air quality is bad, stay inside with the windows closed.
• If you live or work in an area that’s prone to wildfires,  stay away from the harmful smoke  as much as you’re able. Consider keeping a small stock of masks to wear when conditions are poor. The most ideal masks for smoke particles will be labelled “NIOSH” (which stands for National Institute for Occupational Safety and Health) and have either “N95” or “P100” printed on it.
• If you’re using an air conditioner while outdoor pollution conditions are bad, use the recirculating setting to limit the amount of polluted air that gets inside. 

This story was originally published on November 1, 2016, and has been updated with new information and links.

This NRDC.org story is available for online republication by news media outlets or nonprofits under these conditions: The writer(s) must be credited with a byline; you must note prominently that the story was originally published by NRDC.org and link to the original; the story cannot be edited (beyond simple things such as grammar); you can’t resell the story in any form or grant republishing rights to other outlets; you can’t republish our material wholesale or automatically—you need to select stories individually; you can’t republish the photos or graphics on our site without specific permission; you should drop us a note to let us know when you’ve used one of our stories.

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Williams ML, Beevers S, Kitwiroon N, et al. Public health air pollution impacts of pathway options to meet the 2050 UK Climate Change Act target: a modelling study. Southampton (UK): NIHR Journals Library; 2018 Jun. (Public Health Research, No. 6.7.)

Public health air pollution impacts of pathway options to meet the 2050 UK Climate Change Act target: a modelling study.

Chapter 10 discussion and conclusions.

• Scientific conclusions

Scenario emissions

The two ‘CCA-compliant’ scenarios, NRPO and LGHG, had a high proportion of energy generated through biomass use with a large increase in PM 2.5 emissions of approximately 50%, compared with 2011, and peaking in 2035. Although biomass use was projected to decrease again by 2050, primary PM 2.5 emissions in 2050 were still marginally higher than 2011 levels. The baseline and reference scenarios, which did not meet the CCA target, had lower levels of wood burning.

Both the LGHG and the NRPO had a high degree of switching from petrol and diesel fuels to electric, hybrid and alternatively fuelled vehicles in the UK road transport fleet, leading to reductions of around 90% from transport sector NO x emissions in all scenarios except the baseline. The baseline scenario had higher gas and biomass consumption in CHP plants compared with other scenarios, as well as no obligation to meet the CCA target, and this lead to increased NO 2 exposure. In the transportation sector, despite the exhaust emission reductions, the UKTM projections show large increases in traffic activity with car and heavy goods vehicle kilometres projected to increase by roughly 50% in all the scenarios and vans by a factor of about 2. This leads to a pro-rata increase in PM emissions from brake and tyre wear and resuspension of road dust, although these are uncertain as we have assumed in future that the emissions factors will remain at current levels. Consequently, non-exhaust emissions could be the dominant source of primary PM from vehicles in future, increasing PM 10 by about 15% compared with 2011 in the NRPO scenario, for example. This is more of an issue for PM 10 , as the non-exhaust emissions are coarser in size.

Pollutant concentrations

Annual mean concentrations of NO 2 are projected to decrease by about 60% in the LGHG scenario and by ≈50% in the NRPO scenario across the whole of GB and in London, but only by ≈20% across GB and ≈42% in London in the baseline scenario.

Annual mean PM 2.5 concentrations are also projected to fall by around 40% in the top 25% of grid squares, but by only ≈25% in the highest areas. However, concentrations of primary PM 2.5 are projected to increase in 2035 in the NRPO and LGHG scenarios, by around 30–60% in the more polluted grid squares, as a result of the increase in biomass use. By 2050, in those two scenarios, levels are only slightly lower than 2011 values and in the highest grid square are very similar to 2011 concentrations. If this amount of primary PM 2.5 were to be removed, by avoiding the high use of biomass, total PM 2.5 concentrations could fall even further than projected, down by ≈50% in the highest areas compared with ≈25% reduction with the increased biomass use.

Total PM 10 concentrations are projected to increase in 2035 in many areas of the UK in both the LGHG and NRPO scenarios, despite the reduction in secondary PM precursors, because of the increased use of biomass and the increased non-exhaust emissions from transport. PM 10 levels decrease again by 2050, but remain only about 15% smaller than 2011 in the more polluted areas of GB. This is a small reduction and is not larger because of the increasing contribution from non-exhaust emissions. This is of concern as these emissions are potentially toxic.

The reductions in NO x emissions result in increasing annual average O 3 concentrations in urban areas, leading to higher exposures using the metric recommended by COMEAP for short-term impact on mortality. In contrast, all scenarios show reductions in the metric suggested by the WHO for long-term O 3 exposure impact on mortality.

Both O 3 and NO 2 are strong oxidising agents and can play a role in oxidative stress in the human body. This can be quantified through the use of the metric O x or oxidant (O x  = O 3  + NO 2 ), which has been shown to be associated with adverse health outcomes. Annual average levels are projected to remain virtually constant to 2050. The significance of this for health is that the balance of O x will shift to O 3 as NO 2 reduces; the former is the more powerful O x so that the oxidising power of the urban atmosphere in the UK will increase with potentially increased adverse health effects, assuming that the global background of O 3 remains broadly constant.

Health impact

We have calculated impact arising from long-term exposures to the pollutants PM 2.5 , NO 2 and O 3 , on mortality, using a life table approach to calculate the loss of life-years in each of the scenarios. This now incorporates birth projections, projected improvements in mortality rates and mortality rates at local authority level. The two scenarios which achieve the CCA target result in more life-years lost from long-term exposures to PM 2.5 beyond the carbon policies already in place and the levels of PM 2.5 still result in a loss of life expectancy from birth in 2011 of around 4 months. This is an important opportunity lost and arises from the large increase in biomass use peaking in 2035. Our estimates suggest that in the more highly polluted areas of GB, total PM 2.5 concentrations could reduce by as much as 50% without the biomass contribution.

There is currently some uncertainty over the role of NO 2 vis-à-vis PM 2.5 , but using the CRFs currently suggested by COMEAP, reduced long-term exposures to NO 2 lead to more life-years saved and an improvement of 2 months in loss of life expectancy from birth in 2011 in the ‘CCA-compliant’ scenarios compared with the baseline scenario, with the largest benefits arising from the most ambitious scenario LGHG.

Evidence for impact on mortality of long-term exposures to O 3 is increasing, although using the quantification recommended by WHO we estimate life-years lost from this exposure to be smaller by factors of ≈6 and ≈3–4, than those from PM 2.5 and from NO 2 , respectively, if no threshold is assumed for NO 2 . However, the short-term O 3 exposure metric recommended by COMEAP suggests the number of DBF in a year could be around 22,000 compared with 29,000 from long-term PM 2.5 exposures.

However, it should be noted that the distinction between effects attributable to NO 2 and those attributable to PM 2.5 and the issue of how if, at all, one might add the effects of both pollutants is still a matter of some uncertainty. COMEAP is currently in the process of preparing a report on this subject, unpublished at the time of writing.

The issue of a no-effects threshold is also very important on quantifying the impact of O 3 concentrations. The long-term exposure metric recommended by WHO in the HRAPIE project 95 as a sensitivity study included a threshold of 35 p.p.b. or 70 µg/m 3 and resulted in an impact on life-years lost much smaller than those of PM 2.5 and NO 2 . However, the short-term exposure metric recommended by COMEAP did not incorporate a threshold, and a rough calculation suggests that the impact from this metric of O 3 concentrations could lead to the number of DBF of a similar order to that for PM 2.5 , approximately 20,000 from O 3 exposure compared with 29,000 from PM 2.5 .

We also investigated the effect of the changing concentrations on exposures in different socioeconomic classes. We observed differences in air pollution levels in subpopulations for all analysed pollutants and for each geographical area. Differences in exposure were most marked for NO 2 for ethnicity and for socioeconomic deprivation. Wards with higher proportions of non-white residence and higher deprivation are expected to be closer to roads and, therefore, exposed to these higher NO 2 levels. The ratios of exposures in white and non-white populations were much larger than those for the most deprived populations compared with least deprived populations in GB and Wales, but slightly smaller in London. Relative differences between most and least deprived populations were highest in Scotland, closely followed by London; relative differences in Wales were the smallest.

All future scenarios reduced the absolute levels of pollution exposure in all deprivation quintiles across GB, except in those cases in which there is a large increase in biomass burning. Differences in exposure between the most and least deprived populations remain in all scenarios, most clearly for NO 2 , in which there is little difference between the baseline scenario and the NRPO scenario.

• Limitations of the research

Although we have presented an advanced and detailed modelling study of the air pollution impact on health from climate policies, there are inevitable limitations to the work. We used the complex UKTM energy model as this represents a much more detailed method of generating energy scenarios than our original proposal. Because of this we were able to run only a limited number of scenarios. A wider range of pathways to the CCA would have potentially quantified a larger degree of health improvements in future years. The complexity of the UKTM model and the system we have built requires significant computer resources so that it is impracticable to undertake a range of sensitivity analyses around the economic parameters and energy and transport futures in the UKTM model.

Air quality modelling is always limited by several factors, the most important of which is the accuracy of the emissions inventory input. We improved the existing inventories using the most up-to-date information, but there are inevitably limitations to this knowledge. Equally, our understanding of the mechanisms of particle formation is developing continuously and, although we have used the best available chemical/physical mechanism of particle formation, there are still uncertainties involved here.

The health impact calculations are limited by the uncertainty in the numerical coefficients relating health outcomes to air pollutant concentrations, although to a degree we have allowed for this via the confidence intervals incorporated in the epidemiological studies. An important limitation is the extent to which the science supports an independent effect of NO 2 compared with PM 2.5 and the degree of overlap between the two pollutants in the association with adverse health outcomes. The review of the evidence by COMEAP, due to be published near the time of writing, had not appeared as this report was finalised.

Although improving the modelling scale down to 20 m in urban areas is an important advance in picking up exposure contrasts (particularly close to roads), the health impact methodology used is not, at this stage, able to take full advantage of this. In order to be able to use routinely available statistics on population and mortality by age group, concentrations were averaged up to ward level. Depending on how small-scale variations in population and mortality line up with variations in pollutant concentrations (particularly NO 2 ), results could differ if finer-scale inputs were used for population and mortality as well as concentration.

• Uncertainties

Uncertainties in emissions and air quality modelling

The energy scenario modelling represents a series of hypothetical futures, and, if we were trying to predict actual future energy use in a forecasting sense, we would have needed to explore the uncertainties around the economic forecasts, for example. However, in the sense that we have used the projections – in a ‘what if?’ sense – then these uncertainties become less relevant.

The development of a new energy and air quality model has been a significant undertaking and represents an important step forward as a policy development tool. The inputs to the model system are numerous and the uncertainties are difficult to test in a comprehensive way, and, although we have started to look at methods to test the CMAQ model uncertainties for O 3 predictions, these methods have not been used in the present work.

In lieu of a detailed uncertainty analysis we have provided results of a model evaluation exercise across GB using 80 measurement sites. Using the criteria in a recent model evaluation exercise, we have confidence that the combination of the WRF meteorological model, emissions and CMAQ/ADMS air pollution models is able to reproduce 2011 and 2012 concentrations of NO X , NO 2 , O 3 , PM 10 and PM 2.5 at spatial scales, from 10 km across the UK, down to 20-m scale in urban areas. Furthermore, comparison with PM component measurements (nitrate, sulphate, OA, etc.) from the London 2012 ClearfLo campaign show good agreement, which is encouraging both from a model chemistry point of view, but also because it supports the introduction of new emissions to the model, such as domestic wood burning, cooking and diesel IVOCs. The UKTM model has also been evaluated against 2010 energy statistics and WRF assessed against 169 UK Met Office measurement sites.

There is uncertainty in future emissions predictions over whether we use energy-related activity data from the UKTM model or emissions factor assumptions, although for the latter we have used UK NAEI 2030 emission factors as far as possible.

Specific examples include uncertainties in our understanding of PM 10 non-exhaust emissions, which are assumed to increase pro rata with vehicle kilometres to 2050. This assumption may change as some private cars become lighter, are fitted with lower rolling resistant tyres and use regenerative braking, whereas delivery vehicles become heavier, and as all vehicles are subject to increased city congestion and there are ongoing changes to the materials used in brakes and tyre manufacture. Without regulation of these sources future predictions should be considered with caution.

Furthermore, the treatment of domestic wood burning emissions makes assumptions regarding the mix of wood burning appliances resulting in a 19% reduction in PM emissions per kilogram of wood burnt, as a result of the introduction of stoves complying with emission limits in the Ecodesign Directive (53% reduction in PM emissions compared with existing wood burners) and large pelletised domestic appliances (93% reduction in PM emissions compared with existing wood burners) in the UK appliance stock. Another important uncertainty is the location of CHP stations, which we have assumed is the same as existing UK locations for this source (i.e. in northern UK cities). Although this is not unreasonable, the introduction of CHP is already happening in other cities such as London and, although not likely to change the total emissions in our model, will possibly spread the impact away more widely than we have assumed.

Finally, although there will always be uncertainty in future predictions, the project aims were to provide alternative future scenarios, pointing out the potential for undesirable air pollution impacts within climate change policy and accepting that a large range of outcomes are possible.

Uncertainties in health and inequalities

Calculations were done using the confidence intervals (or plausibility intervals in the case of PM 2.5 ) to give one indication of a range of possible answers. For PM 2.5 this gave a range for the life-years lost or gained from one-sixth to twice the result for the central estimate. This was in line with the range for the originating CRF. The proportion relative to the central estimate varied very slightly – because of the non-linearities in the calculations. This range is not that for a 95% confidence interval. The original COMEAP recommendations included wider uncertainties than just those relating to statistical sampling. In addition, uncertainties in other inputs are not included. The range for the differences between scenarios was derived by subtracting the lower ends of the ranges for each scenario from each other – this probably overestimates the range. The impact of the spatial scale of the modelling was investigated, but not other issues so far. Some inputs are well established (e.g. population and deaths data), but, even in that case, assumptions are required, for example inferring distribution by age at small local areas from distributions at a wider geographical scale. The uncertainties in the modelling data have been discussed above but have not, so far, been propagated to the health impact calculations. In principle, this could be done, but would involve a much larger resource than was available in this project. There are a variety of versions of mortality rate improvement projections and birth projections – we have used only the central ones. Migration was not included and it is very unclear at present in which direction this will go.

Many of the same issues apply to the calculations for NO 2 (with and without a cut-off point). In terms of the 95% confidence interval of the CRFs, the results varied from 41%/42% of the central estimate to 1.6 times the central estimate. This only represents one aspect of the uncertainty. Results can be sensitive to the choice of cut-off point.

As described in Chapter 8 , we assumed that deprivation and ethnicity patterns at the small area level observed in 2011 are representative for the years 2035 and 2050. This assumption is based on studies which have shown that, in particular, deprivation patterns are fairly stable over time. We used this approach because no information on future deprivation or ethnicity patterns is available that far into the future. Uncertainties associated with such future sociodemographic prediction would be expected to not be dissimilar to those associated with our approach.

Inevitably, assumptions have to be made when projecting into the future. Inclusion of projected mortality improvements and birth projections improved this, compared with assuming baseline mortality rates and births remaining the same. However, these projections themselves are uncertain. In addition, we did not include projections of migration at this stage.

The project’s contribution to advances in knowledge

This project has, for the first time in the UK, delivered a sophisticated tool to enable the explicit calculation of public health impact arising from future energy strategies in GB using a state-of-the-art air quality model with an energy systems model used to inform government policy on greenhouse gas mitigation. This represents a major improvement over previous approaches to the impact of greenhouse gas emissions. Our work has established a method of calculating public health impact of air pollution resulting from climate policies through the full ‘impact pathway’ approach rather than the cruder, more approximate, ‘damage cost’ approach. The latter approach has been used to date by government in the UK to appraise climate policies; it relies on simply assigning a monetary value to a unit of air pollution emission. Consequently, there is no explicit calculation of pollution concentrations in the air, or of the impact on mortality and morbidity. Our system now allows that to be done in a linked system beginning with the economic model of the British energy system, through a sophisticated air quality model to a detailed life table model for calculating impact on health, on exposures in socioeconomic classes and for calculating economic impact. Moreover, the system we have developed allows this impact to be calculated at the finest spatial resolution yet achieved in GB, in which we model the rural areas at 10 km and major urban centres at 2 km or as fine as 20 m.

The science of air quality and of PM has continued to evolve during the life of the project. During the study it was necessary for us to incorporate emerging research on the sources of PM from cooking sources that were not previously included in emission inventories in GB. We have also built on King’s College London’s expertise in understanding the contribution of wood (biomass) burning to air quality to improve the inventory of emissions from this source. We were also able to enhance our model to treat the major British cities at a spatial resolution of 20 m, where previously we had been able to do this only for London. We have evaluated this improved air quality model and shown it to behave well against accepted criteria.

During the course of the project, we formed a collaboration with the Institute for Sustainable Resources at UCL to allow us to link the UKTM energy systems model with our air quality model and our health impact capability. This formed a major advance and the link now establishes a credible system to assess the impact of energy futures and climate policies in GB.

There are several important policy messages which arise from this project. The CCA target, in principle, offers a great opportunity to make very large reductions in air pollution emissions as the UK energy system is decarbonised. However, the PM 2.5 emissions from the large increases in residential and CHP biomass use and the increase in non-exhaust PM emissions from transport in the two CCA-compliant scenarios we have studie mean that PM 2.5 and PM 10 concentrations do not fall as much as they would otherwise have done without the biomass use. This increase in biomass use has resulted in the finding that the CCA-compliant scenarios result in more life-years lost than the baseline scenario which incorporates no further climate action beyond that already in place.

Solutions to improve air quality impact on health could include measures to discourage the use of biomass in small installations, or to increase the stringency of the emission limits in the Ecodesign Directive. The related study by Lott et al. , 33 using the damage cost approach, carried out a calculation including damage costs for biomass use to attempt to account for the public health impact. This succeeded in reducing the use of biomass in the hypothetical calculation. In reality, measures to discourage biomass use would probably be best delivered through revisions to the renewable heat incentive. In terms of improving air quality and minimising the impact on public health, wood burning, if it were to be used at all, would be best deployed in large, efficient power stations rather than small-scale domestic or CHP use. Fiscal measures in the renewable heat incentive to encourage this shift would have benefits to public health without necessarily compromising the achievement of the CCA target.

Non-exhaust emissions of PM 10 , and to a lesser extent PM 2.5 , are projected to increase significantly by 2050 as traffic activity increases. The precise agents in tyre and brake wear and resuspended dust responsible for the potential toxicity of these emissions are, as yet, unclear, so reformulation of these products would need to await more clarification from toxicological research. However, in the meantime, the obvious solution to ameliorate potential impact from all emissions from road transport here would be to discourage traffic use, particularly in urban centres.

On the positive side, electrification of the road transport fleet results in large reductions in the potential adverse impact on health from NO 2 and potential compliance with legal standards. This will also have benefits for PM concentrations and will, to a limited degree, offset the impact of any continued increase in biomass use.

The use of economic appraisal provides a mechanism for assessing the efficacy of measures for further action, permitting direct comparison of costs and benefits of measures, and enabling collation of a variety of different types of effect. As shown above, economic damage associated with air pollution in the UK is substantial and will remain so over the period covered by the scenarios considered here. It is noted that the UK approaches to valuation appear highly conservative compared with assumptions followed in the wider international literature.

Further research with the linked UKTM and our air quality model, CMAQ-Urban, could investigate other possible scenarios which achieve the CCA target and which could minimise the problem with residential and CHP biomass use and the impact of non-exhaust road transport emissions.

• Recommendations for future research

The system we have developed links together a sophisticated energy system model – used by government in the UK – with a detailed chemical–transport model for air quality, health impact calculations and assessments of exposures and impacts in different socioeconomic classes. It also allows the monetary valuation of this impact on health. Because of the complexity of the system we have been able to run only a small number of scenarios and, although we have demonstrated some significant issues for future climate change mitigation measures, there is still scope to address optimal pathways for attaining the CCA target by minimising the impact on air quality and public health.

The work has shown that trends in different fractions of the atmospheric particle mix may be different in future. Primary particles (containing known carcinogens) may increase, whereas secondary particles may decrease. This highlights the importance of studies to elucidate the differential toxicity of different particle fractions.

The work has shown that, with increased penetration of ultra-low and zero-emissions road vehicles, concentrations of NO 2 will decrease by large amounts. The precise role of NO 2 , compared with that of PM 2.5 and other pollutants, in affecting human health is still uncertain. More clarity is needed here before any health benefits from reductions in NO 2 can be confidently quantified.

The effects of long-term exposure to air pollution on mortality generally dominate cost–benefit analysis, but a full investigation of the health impact would involve quantifying the potential effects on a wider range of health outcomes. In addition, further sensitivity analyses on the data inputs and assumptions regarding CRFs (e.g. effect modification) would be helpful. There is a need to explore how using population and mortality inputs at a finer geographical scale affects the result. More meta-analyses of epidemiological studies on PM 2.5 and NO 2 will also be useful.

• Cite this Page Williams ML, Beevers S, Kitwiroon N, et al. Public health air pollution impacts of pathway options to meet the 2050 UK Climate Change Act target: a modelling study. Southampton (UK): NIHR Journals Library; 2018 Jun. (Public Health Research, No. 6.7.) Chapter 10, Discussion and conclusions.
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Home > Books > Air Pollution - Latest Status and Current Developments

Introductory Chapter: Air Pollution – Understanding Its Causes, Effects, and Solutions

Submitted: 11 April 2023 Published: 20 September 2023

DOI: 10.5772/intechopen.111588

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Air Pollution - Latest Status and Current Developments

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Author Information

Murat eyvaz *.

• Department of Environmental Engineering, Gebze Technical University, Kocaeli, Turkey

Ahmed Albahnasawi

Motasem y. d. alazaiza.

• Department of Civil and Environmental Engineering, A’Sharqiyah University, Ibra, Oman

*Address all correspondence to: [email protected]

1. Introduction

Air pollution is a significant environmental and public health issue that affects millions of people worldwide. It is caused by a variety of human activities, including industrial processes, transportation, and energy production, among others. The problem is particularly severe in urban areas, where population density and economic activity contribute to high levels of pollution. Air pollution can have significant health impacts, including respiratory diseases, cardiovascular diseases, and cancer, among others. In addition to its impact on human health, air pollution can also have adverse effects on the environment, including on plant and animal species and ecosystems.

Air pollution levels vary greatly between regions and countries and are influenced by a range of factors such as climate, topography, and population density. In urban areas, air pollution is often higher due to the concentration of anthropogenic sources, such as traffic, industry, and power generation. For example, a study conducted in Beijing, China, found that the city’s air pollution was primarily caused by the burning of fossil fuels, including coal, oil, and natural gas [ 1 ].

Air pollution is also a major environmental concern in developing countries, where industrial activities and transportation infrastructure are expanding rapidly. In India, for instance, air pollution is estimated to cause over one million premature deaths each year [ 2 ]. The country has implemented several measures to address air pollution, including the National Clean Air Program, which aims to reduce particulate matter concentrations by 20–30% by 2024 [ 3 ].

This book aims to provide an overview of the current state of air pollution and the latest developments in this field. It covers a range of topics, including the sources and types of air pollutants, their effects on human health and the environment, and the policies and technologies aimed at reducing emissions and improving air quality. It is intended for students, researchers, policymakers, and anyone interested in understanding and addressing this critical environmental issue.

2. Sources of air pollution

There are many sources of air pollution, including both human-made and natural sources. Human-made sources of air pollution include industrial activities, transportation, energy production, and agricultural practices. These sources release a range of pollutants, including particulate matter (PM), nitrogen oxides (NOx), sulfur dioxide (SO2), volatile organic compounds (VOCs), and carbon monoxide (CO), among others. Natural sources of air pollution include wildfires, dust storms, and volcanic eruptions, among others.

3. Health impacts of air pollution

Air pollution can have significant health impacts, particularly for vulnerable populations such as children, the elderly, and individuals with pre-existing health conditions. The World Health Organization (WHO) estimates that air pollution is responsible for approximately seven million premature deaths annually worldwide [ 4 ]. Exposure to air pollution can lead to a range of health problems, including respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD), cardiovascular diseases, and cancer, among others. Long-term exposure to air pollution has also been linked to cognitive decline and neurological disorders [ 5 ].

Recent research has highlighted the health impacts of air pollution, particularly the impact of PM. A study published in The Lancet Planetary Health found that exposure to PM2.5 (fine particulate matter with a diameter of less than 2.5 micrometers) is responsible for approximately 500,000 premature deaths annually in Europe [ 6 ]. Another study published in Environmental Research estimated that long-term exposure to PM2.5 is responsible for 6.7 million premature deaths annually worldwide [ 7 ]. Another studies have highlighted the impact of air pollution on cognitive function, with exposure to high levels of air pollution linked to decreased cognitive performance and an increased risk of dementia [ 8 , 9 ]. Other studies have focused on the impact of air pollution on plant and animal life, with findings showing that air pollution can have significant negative effects on ecosystems and biodiversity [ 10 ].

4. Environmental impacts of air pollution

Air pollution can also have adverse effects on the environment, including on plant and animal species and ecosystems. Acid rain, for example, is a type of air pollution that can have significant impacts on forests, lakes, and rivers. Acid rain occurs when sulfur dioxide and nitrogen oxides are released into the atmosphere and react with water, oxygen, and other chemicals to form acidic compounds. These compounds can then fall to the ground as acid rain, damaging forests, lakes, and rivers and harming plant and animal species.

5. Climate change and air pollution

Air pollution is also a significant contributor to climate change. Greenhouse gases, such as carbon dioxide (CO 2 ), trap heat in the atmosphere, causing global temperatures to rise. Human activities, including the burning of fossil fuels, transportation, and industrial processes, contribute to the release of greenhouse gases and the warming of the planet. Climate change can have significant environmental and social impacts, including rising sea levels, increased frequency and intensity of natural disasters, and food and water scarcity, among others.

6. Current developments in air pollution control

Governments, businesses, and individuals can all play a role in reducing air pollution through policies, investments, and behavior change. Many countries have implemented policies to reduce air pollution, including regulations on industrial emissions, cleaner energy standards, and the promotion of public transportation and active transportation options. One such initiative is the Paris Agreement, which aims to limit global warming to below 2°C above pre-industrial levels by reducing greenhouse gas emissions [ 11 ]. Another initiative is the World Health Organization’s Global Ambient Air Quality Database, which provides information on air quality levels in cities and countries worldwide [ 4 ].

Technological developments and innovations are also contributing to the fight against air pollution. For example, electric vehicles and renewable energy sources are becoming increasingly popular and affordable, reducing the need for fossil fuels and decreasing emissions. Advances in monitoring technology, such as air quality sensors and satellite imagery, are also providing more accurate and real-time data on air pollution levels.

7. Challenges and future directions

Despite these promising developments, there are still significant challenges to addressing air pollution. In many parts of the world, particularly in developing countries, air pollution levels are still high, and policies and regulations may not be adequately enforced. The problem of air pollution is also complex, and solutions may require significant changes in infrastructure, behavior, and policy.

There is a growing recognition of the need for a coordinated, global effort to address air pollution. The United Nations Sustainable Development Goals include a target to substantially reduce the number of deaths and illnesses from air pollution by 2030. Achieving this target will require a range of strategies, including investments in clean energy, improvements in public transportation, and more effective regulation of industrial activities. Moreover, cleaner technologies, such as electric vehicles and renewable energy sources, as well as the adoption of policies aimed at reducing emissions from existing sources [ 12 ] were proposed. In addition, there is a growing interest in the use of green infrastructure, such as urban forests and green roofs, to improve air quality in urban areas [ 13 ].

8. Conclusion

Air pollution is a significant environmental and public health issue that affects millions of people worldwide. It is caused by a variety of human activities, including industrial processes, transportation, and energy production. Air pollution can have significant health impacts, particularly for vulnerable populations such as children, the elderly, and individuals with pre-existing health conditions. In addition to its impact on human health, air pollution can also have adverse effects on the environment, including on plant and animal species and ecosystems. Technological developments and innovations are contributing to the fight against air pollution, but more work is needed to address the problem. Governments, businesses, and individuals can all play a role in reducing air pollution through policies, investments, and behavior change.

• 1. Wang L, Zhang F, Pilot E, Yu J, Nie C, Holdaway J, et al. Taking action on air pollution control in the Beijing-Tianjin-Hebei (BTH) region: Progress, challenges and opportunities. International Journal of Environmental Research and Public Health. 2018; 15 (2):306. DOI: 10.3390/ijerph15020306
• 2. Landrigan PJ, Fuller R, Acosta NJR, Adeyi O, Arnold R, Basu NN, et al. The lancet commission on pollution and health. Lancet (London, England). 2018; 391 (10119):462-512. DOI: 10.1016/S0140-6736(17)32345-0
• 3. Ministry of Environment, Forest and Climate Change. National Clean Air Programme (NCAP). Government of India. New Delhi, India. Available from: https://moef.gov.in/wp-content/uploads/2019/05/NCAP_Report.pdf . 2019 Access date: 05/04/2023
• 4. World Health Organization. Ambient (outdoor) pollution. 2022. Retrieved from: https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health [Access date: 03/04/2023]
• 5. Jiang XQ , Mei XD, Feng D. Air pollution and chronic airway diseases: What should people know and do?. Journal of Thoracic Disease. 2016; 8 (1):E31-E40. DOI: 10.3978/j.issn.2072-1439.2015.11.50
• 6. Lelieveld J, Klingmüller K, Pozzer A, Pöschl U, Fnais M, Daiber A, et al. Cardiovascular disease burden from ambient air pollution in Europe reassessed using novel hazard ratio functions. European Heart Journal. 2019; 40 (20):1590-1596. DOI: 10.1093/eurheartj/ehz135
• 7. Cohen AJ, Brauer M, Burnett R, Anderson HR, Frostad J, Estep K, et al. Estimates and 25-year trends of the global burden of disease attributable to ambient air pollution: An analysis of data from the global burden of diseases study 2015. Lancet (London, England). 2017; 389 (10082):1907-1918. DOI: 10.1016/S0140-6736(17)30505-6
• 8. Zhang X, Chen X, Zhang X. The impact of exposure to air pollution on cognitive performance. Proceedings of the National Academy of Sciences of the United States of America. 2018; 115 (37):9193-9197. DOI: 10.1073/pnas.1809474115
• 9. Cai R, Zhang Y, Simmering JE, Schultz JL, Li Y, Fernandez-Carasa I, et al. Enhancing glycolysis attenuates Parkinson’s disease progression in models and clinical databases. Journal of Clinical Investigation. 2019; 129 (10):4539-4549
• 10. Lovett GM, Tear TH, Evers DC, Findlay SE, Cosby BJ, Dunscomb JK, et al. Effects of air pollution on ecosystems and biological diversity in the eastern United States. Annals of the New York Academy of Sciences. 2009; 1162 :99-135. DOI: 10.1111/j.1749-6632.2009.04153.x
• 11. United Nations. Paris agreement. 2015. Available from: https://unfccc.int/sites/default/files/english_paris_agreement.pdf [Access date: 03/04/2023]
• 12. Sims R, Schaeffer R, Creutzig F, Cruz-Núñez X, D’Agosto M, Dimitriu D, et al. Transport. In: Edenhofer O, Pichs-Madruga R, Sokona Y, Farahani E, Kadner S, Seyboth K, editors. Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovern-Mental Panel on Climate Change. Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press; 2014
• 13. Nowak DJ, Hirabayashi S, Bodine A, Hoehn R. Modeled PM2.5 removal by trees in ten U.S. cities and associated health effects. Environmental pollution. 2013; 178 :395-402. DOI: 10.1016/j.envpol.2013.03.050

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Table of contents.

To live, we need to breathe. To breathe, we need fresh air. Fresh air is one of the basic and essential things we need to live on earth. Fresh air is equally important to every one us as food and water. Even plants need oxygen to convert food into energy. From these things, we can understand the importance of oxygen and fresh air. A place without oxygen will be a dead zone with no humans, animals, and plants. Without oxygen, nobody can survive on earth.

All these facts point the fingers at the importance of keeping air pollution-free. But the truth is, the air is getting polluted at a massive rate every day. There are hundreds of causes. In these, there are some which are very harmful to us. But how can we reduce the rate of air pollution? Well, there are different ways that we could try to stop air pollution. Before that, let us find out what are the utmost causes of air pollution. Here are they. 

What Do We Mean By Air Pollution?

It’s simple. Air pollution refers to the release of pollutants into the air like Nitrogen Oxide, Volatile Organic Compounds, Carbon Dioxide, Sulphur Oxide, dioxins, and other harmful gases. Once these gases are released, they become a colossal threat to the environment and human health.

How Do We Know the Quality of Air?

The purity of air measured using an AQI thermometer that runs on a scale from 0 to 500. The AQI refers to Air Quality Index. It measures how pure or polluted the surrounding air is. If the numeric value on the scale is between 0-50, the quality of the surrounding air is considered healthy and satisfactory. As the values increase, the quality of the air decreases. If AQI is showing a value of 500, that means you are standing in a hazardous surrounding. Have a look at the AQI chart below for more details.

Major Causes Of Air Pollution

It is well known to everyone how air pollution happens. It happens in many ways. Sometimes careless and reckless human activities lead to the major reasons for air pollution. Even though, here are some of the common causes of air pollution.

Burning of Plastic Wastes.

How do we avoid plastics from our houses? Either we throw them or light them up, right? These careless acts will lead to the worst pollution ever. Burning them releases toxic gases like dioxins, furans, mercury, and polychlorinated. These gases are a threat to the atmosphere, vegetation, humans, and animal health. If we throw them out, they can remain in the soil for 20-500 years before fully decomposing based on the material and structure. Over these years, it pollutes the soil and harms the earth. 

So, burning and throwing plastic does not work and leads to air pollution or soil pollution in the long term perspective. Then what will we do? Well, we can recycle and reuse plastic to an extent. But once the plastic is melted and reformed into new products, the quality of plastic gets reduced. In addition, the quality of plastic will keep reducing with every successive recycling. Furthermore, recycling is limited to a number 3 or 4 times because of the quality compromise of plastic. 

In fact, we only have a limited number of opportunities in the case of plastic. Either we reduce the use of plastic or recycle and reuse them as much as we can. 

Limiting the use of plastic seems more practical and smooth in our day-to-day life. There are many instances where we can reduce the use of plastic. Here are some of the tracts where we can instantly act to limit the usages of plastic

• Use cloth bags instead of plastics bags while going to the shops.
• Use paper plates and tumblers instead of plastic ones when you arrange a tea party or get-togethers. 
• Use paper straws in restaurants and coffee shops.
• Use paper bottled soft drinks.

There are more and more situations where we can reduce the unnecessary use of plastic covers and materials. It can turn out well when more people come forward with the same mindset of bringing down plastic use. 

Are there any alternatives for plastic?

Yes, there are. But literally, there are no materials with the exact matching properties with plastic. For instance, properties like durability, strength, water-resistant, lightweight, and inexpensive are rare to find in materials without polymer as an ingredient. Scientists and researchers are trying to formulate materials with the matching properties as plastic but with less pollution.

As said earlier, there are many instances where we can reduce the use of plastic and always try to avoid it as much as we can. Even if they are baby steps towards reducing plastic, take it and help our environment. Moreover, be a part of keeping the city and your premises clean.

Industrial Emission

Industries play a colossal role in all kinds of pollutions. They contribute almost one-third to the overall when we compare industrial pollution with other causes. Industries will be the 2nd largest cause of air pollution, water pollution, and sound pollution. Pollutants like carbon monoxide, Nitrogen dioxide, and Sulfur dioxide are released when they operate factories and industries. The volume of pollutants released into the atmosphere is way more than we imagine and the problems they can make are huge.

It is necessary to know where the pollution happens and who pollutes the air the most. Studies say that industries that produce electricity pollute the atmosphere more than any other industry.

A considerable amount of pollutants is kicked from the industries when the continuous burning of fossil fuels happened. These emitted gases make the most of the troubles to the ozone layer and cause ozone layer depletion. We need both electricity and the earth. We can not avoid one or the other for any reason. The only way is to protect both without harming each other. The only solution for this will be the rise of green energy. Only the challenge facing is the continuous supply of energy. Green energy like solar and wind are very cost-effective and pollution-free when comparing to the traditional ones.

Each and every individual can contribute and can be a part of saving the earth from air pollution and global warming. Switch to green energy as much as we can and reduce the consumption of traditional electricity from the government or private companies. Nowadays, everybody has inverters in the home as a standard facility. It will not cost you much to connect 2 or 3 solar panels to the battery and save 60% power usage from the traditional electric supply.

How can we reduce industrial air pollution?

As we said earlier, industries and factories are essential for the growth of the people and nation. We can’t stop factories in the name of air pollution. What we can do is, we can find some ways to reduce the amount of air pollution. For instance, we should try to convert these harmful gases to regular gases with the help of proper techniques and setups.

Most importantly, people living near industrial areas are very likely to have many allergies and lung diseases. Always wear a mask when you are going out or going near industrial and factory areas. If you are working in an industrial area, always wear a mask and other safety gear to ensure maximum safety.

Wildfires can take place at any time. It is an unplanned and uncontrolled fire caused by lightning strikes. As the name says, it occurs largely in forest areas. Mostly, the lighting strikes on the trees, branches, dry grass, and then the fire is generated. Eventually, this fire will spread to other trees, branches, and grasses and becomes wildfires, and causes air pollution.

Wildfires are common forested areas of the United States and Canada. It is one of the causes of air pollution, deforestation, and animal extinction. In a wildfire, many animals lose their lives and shelter. Some get burns and wounds in the running through the wildfire. 

All these will continue until fire settles down. Sometimes it takes 2-3 days to settle down completely. But in the end, we lose animals, trees, the environment, and what not?

Also, sometimes the causes of wildfire can be different. Sometimes it happens due to the carelessness of people living around the forest. For instance, even trash burning and campfires can spread fire if not concerned well. So it is always recommended to take precautions while doing wildfire potential activities.

Wildfires get worse when unattended. If you notice any fires or burns that need attention, call the authorities. Sometimes the fire can be controlled before getting worse.

Transportation

Transportation holds a neck-to-neck position with industries in the rate of air pollution. As we all know, the number of vehicles on the road is increasing day by day. Just look around, we could see houses with more than three vehicles even if they don’t need all of them. As the number of vehicles increases, the rate of pollution also tends to be increased. Old model vehicles are more likely to produce more pollution than new ones. Because when the vehicles get older and older, the amount of carbon emission increases. The rate of pollution is still on the rise even after the government and authorities made pollution laws strict. 

Every country has its own vehicle emission standards or norms for the safety of the environment and people living in the country. But still, transportation holds the position for the majority of air pollutions happening around the world.

How can we reduce pollution caused by vehicles?

Earlier, it was challenging to find an alternative for fuels like petrol or diesel. Right now, technology has improved – researchers found a better alternative solution for the petrol and diesel engines for automobiles. Yes, they are EV’s. Electric vehicles are completely different from traditional vehicles. They are pollution-free and highly efficient than fuel engines. Electric vehicles can be charged from the house or charging stations in and around the city. EV’s have 5x efficiency more than the regular diesel or petrol-fueled automobiles and 4x lesser reduced pollution.

EV’s are on the rise. By 2025, at least 50% of the new vehicles coming out from the factories will be electric vehicles. It will seriously help to reduce the rate of pollution to some extend. People will switch to EV’s when companies launch better models with luxury and comfort.

It may sound crazy to most of us. But think about walking a little every day and avoid taking cars or bikes for smaller distances. Or, use a bicycle to travel nearby. It will help us to improve both our health and the earth’s health.

What are the health issues due to air pollution?

The quality of the air we breathe is very crucial. Poor quality can cause many health diseases in both adults and kids. Especially to the people living in cities, the chances of getting a disease like heart disease, stroke, chronic obstructive pulmonary disease (COPD), lung cancer, and acute lower respiratory infections are very high.

Long-term exposure to polluted air in kids can lead to loss of lung capacity, asthma and emphysema. In addition, senior citizens are more likely to get allergies and breathing difficulties since they are less immune to the conditions. As a precaution to all of these, we can wear a mask while going out and traveling. If you are living in a highly polluted area, consider buying an air purifier for your home. An air purifier can help to improve the quality of air by filtering and thereby enabling a healthy environment inside our home for everyone.

How does air pollution affect environmental health?

The toxic gases also affect the environment in the same way. As the amount of harmful gases increases in the earth, the uncertainty of the environment’s health also increases. Changes in climates like temperature hikes, monsoon pattern shifts, and unexpected cyclones are a few examples. In these, ozone layer depletion is being the most complicated one.

We already know what is an ozone layer, and whats does it do? Let’s recall them for a while. The ozone layer is a part of the earth’s atmosphere, and it absorbs almost all of the sun’s harmful ultraviolet light. Guess what will happen when the ozone layer gets holes. All the harmful rays will fall into the animals, plants, and people on earth through the ozone layer holes. Studies say that by 2064 the ozone layer concentration levels may come to zero if the rate of pollution continues invariably. If that happens, the earth will not be a suitable place to live. The fun factor is, we don’t have any space other than earth to live right now. So, we have to protect the planet from being a desert.

Day by day, the rate of pollution is increasing. The hard truth is, nobody is really caring about the future of our planet. Even the government and authorities are keeping their eyes closed on social issues like global warming, air pollution, and soil erosion. If it keeps going like this, the earth will become uninhabitable.

Protecting the earth from pollutions is not deputed on somebody else. Each one of us should take responsibility and behave sensibly to protect the earth from pollution.

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Epidemiology and Air Pollution (1985)

Chapter: 6 conclusions and recommendations.

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CONCLUSIONS AND RECOMMENDATIONS 191 6 CONCLUSIONS AND RECOMMENDATIONS The Committee reviewed the current status of epidemiologic research on air pollution in the United States. It sought to identify the types of epidemiologic activities that could feasibly be applied to determine the size and nature of the health risks of air pollution, given current magnitudes and patterns. It observed that new approaches will be needed to quantify adverse health effects associated with low concentrations of air pollutants and to separate the impacts of individual pollutants more effectively. The Committee concluded that efforts to specify current and future research questions have been insufficient and that additional investment is needed in research on and development of appropriate investigative tools. It expects the development of new techniques and strategies to make it possible to overcome some of the barriers to the application of epidemiologic approaches. The Committee also concluded that many previous studies had generally failed to recognize the complexity of air pollution research and to integrate all the relevant sciences, including epidemiology, into coherent research plans and programs. The Committee finds that current air pollution can cause acute and perhaps chronic health effects, particularly respiratory effects, in the population of the United States. Respiratory disease is a major cause of work loss and disability. Even though exposure to some major types of pollution has decreased substantially in the last 15 years, exposure to other types has persisted. Improvement has not been uniform in all parts of the country, and some new patterns of air pollution are 

CONCLUSIONS AND RECOMMENDATIONS 192 emerging. The entire population is affected by low concentrations of both indoor and outdoor air contaminants. Even if only a small proportion of very prevalent disease is due to air pollution, the absolute amount of illness that could be prevented by reducing air pollution would be large. Epidemiologic studies can be used to accomplish several things that cannot be accomplished in other ways: • Directly determine whether a public health problem exists. • Estimate the magnitude of the existing public health problem. • Evaluate the impact (health and economic) of decreases in exposure. • Define characteristics of the problem that can guide intervention even before mechanisms are understood. The results of well-conducted epidemiologic research are important in the development and revision of air quality standards and other means of regulating air pollution. It is recognized, however, that regulatory decisions sometimes have to be made before complete observational evidence is available. Although regulatory requirements must influence the definition of research questions and the design of studies, they should not be the sole basis for the development of broad research programs. Regulatory concerns, when narrowly interpreted, revolve around identification of “safe” exposures to individual pollutants--a question that presents few opportunities for studies of their effects on free-living populations. The Committee concludes that epidemiology, if it addresses this question and others mentioned above, can make a unique contribution to the prevention of illness related to air pollution. In view of the above conclusions, the Committee offers the following major recommendation: The Environmental Protection Agency should develop a long-term plan for research on air pollution; and population-based studies, in the form of a program in epidemiology, should be an integral part of that plan. 

CONCLUSIONS AND RECOMMENDATIONS 193 CHARACTERISTICS OF A PROGRAM IN AIR POLLUTION EPIDEMIOLOGY To be productive and cost-effective, the epidemiologic program should have the following four major characteristics: • Maintenance of a capability to interpret and synthesize current knowledge about air pollution and, accordingly, to plan relevant short-term epidemiologic research and make appropriate changes in long-term research. • Inclusion of mechanisms for the creation of multidisciplinary teams to plan and conduct population-based epidemiologic research on the adverse health effects of air pollution. • Means of ensuring stable, long-term epidemiologic research in a context that supports the career development of the researchers and thus limits disruptive changes in personnel. • Exploration of collaboration with agencies that collect or could collect relevant data, after careful consideration of overall long-term data needs. A productive epidemiologic research program must have a dual character with respect to sensitivity to outside forces. Part of the program must be dedicated to responding to rapidly changing conditions that offer important opportunities for. study, to the varying concerns of regulators, and to new information from technologic development and parallel disciplines. In particular, advances in toxicology and clinical research, and epidemiology should be parts of the same framework; advances in any one can drive new efforts in the others. Another part of the program, engaged in long-term research strategies or longitudinal studies, must remain relatively isolated and free from abrupt change, although the incorporation of new elements will sometimes be desirable. It is important that the Environmental Protection Agency (EPA) program staff at all levels include highly trained and experienced epidemiologists, regardless of whether research is conducted intramurally or extramurally. 

CONCLUSIONS AND RECOMMENDATIONS 194 Continuous access to both advice and review from scientists outside the institution will also be greatly needed. Given the constraining and difficult nature of today's questions about air pollution, stable research teams with expertise in several critical fields will be most productive. Epidemiologists in the teams should collaborate with atmospheric scientists, statisticians, and health effects scientists in all phases of research, from study design through interpretation. The present structure of many universities and government research agencies often makes it difficult to arrange such collaboration. Financial and administrative mechanisms that encourage development of these teams must be implemented; and the EPA program staff itself must have a multidisciplinary composition. The value of large data systems developed for reasons other than air pollution studies (such as the National Health and Nutrition Examination Survey, the National Health Interview Survey, and the National Ambulatory Medical Care Survey) as resources in air pollution research should be assessed. Whether modifications in some of them and linkage to air pollution exposure data constitute a feasible and cost-effective research approach that affords very large samples should also be explored. Modification in the routinely collected air sampling data alone might be appropriate, to facilitate use of these data in some types of epidemiologic studies. THE FOCUS FOR RESEARCH For the immediate future, the epidemiologic research program should focus on the following exposures and effects of concern: • Persistent air pollution problems, including the health effects of acid sulfate particles, ozone, nitrogen dioxide, carbon monoxide, lead, and radon. It should be flexible enough to address emerging problems, such as the health effects of products of incomplete combustion and volatile organic chemicals. 

CONCLUSIONS AND RECOMMENDATIONS 195 • Lung disorders in which air pollution might play a role, including chronic obstructive pulmonary disease, asthma, decreased rate of lung growth or increased rate of lung decline with aging, and increased susceptibility to acute respiratory infections. • The quantitative contribution of air pollutants to lung cancer in human populations. For this purpose, it could take advantage of the existing funding arrangement between EPA and the National Cancer Institute for the support of epidemiologic studies of this problem. Many important questions about the “traditional” pollutants remain unanswered. For example, the acute and chronic respiratory effects of acid aerosol and ozone exposures, which might result only from outdoor sources, are not well understood. An extensive population, perhaps in excess of 100 million, is exposed to ambient ozone at high concentrations during the spring and summer. Shifts in coal combustion to the south central states will result in an increase in the area and population exposed to acid aerosols. No systematic epidemiologic study has been designed to assess either the acute or chronic effects of this type of shift in exposure. Exposures to acid aerosols are likely to increase more in rural areas than in urban areas, so it is recommended that consideration be given to locating baseline and followup studies in rural areas. As new automotive fuels, new industries, new fuel sources, new commercial products for the home, and new building ventilation patterns are introduced, they might yield new pollutants and pollution patterns that require epidemiologic evaluation. These changes will result in increased exposures to volatile and particulate organic compounds, radon, carbon monoxide, and other potentially hazardous materials. Indoor air pollution can be a major factor--in some instances the principal factor--in determining total personal exposure (averaged and acute) to air pollutants. Epidemiologic studies must therefore consider indoor or outdoor concentrations, or both, depending on the health response and pollutant being examined. For example, average and peak exposures to nitrogen dioxide are determined primarily by the presence of unvented indoor combustion sources. Peak exposures higher than those in 

CONCLUSIONS AND RECOMMENDATIONS 196 most urban outdoor environments occur often in residences that use unvented gas or kerosene as a cooking or heating fuel. Therefore, to assess the health effects of nitrogen dioxide, EPA should study respiratory infection, pulmonary function changes, and, as soon as possible, biochemical indicators in association with indoor exposures and simultaneous outdoor exposures. There have been important advances in air monitoring instruments and inferential data analysis techniques. Air pollution is a complex mixture of gases, vapors, and particles; epidemiologic studies will often benefit from detailed characterization of its components. For instance, the chemical composition and acidity of size-fractionated particles should be characterized where appropriate. In some cases, new techniques for biologic characterization are also appropriate. Detailed characterization can help to determine the air pollution components most closely associated with health outcomes, potential confounders, and the relative contributions of various sources. The most readily observed health effects of air pollution are in the respiratory system. The proportion of the overall disease burden from common respiratory diseases that is attributable to air pollution has not yet been established. This part of the disease burden includes both the development of disease de novo and the exacerbation of pre-existing disease. Air pollution might have nonrespiratory effects that, although not emphasized in this report, also deserve study. These include neurobehavioral deficits and essential hypertension related to lead exposure, ischemic heart disease related to carbon monoxide, and carcinogenesis and mutagenesis related to various volatile hydrocarbons. Respiratory cancers, which are the most common cause of cancer death in men and will soon be in women, are attributable largely to cigarette smoking. However, attempts to assign proportions of this disease burden to separate causal agents, such as air pollution, are frustrated by the multifactorial and interactive etiology of these cancers. It is particularly important to understand the role of air pollutants in lung cancer, inasmuch 

CONCLUSIONS AND RECOMMENDATIONS 197 as interactive effects might multiply the number of cases that could be prevented by reducing exposures. The limits of an epidemiologic research program depend on the questions under consideration. Only by considering each research question carefully can one understand the limits of investigative methods and discuss them productively. In general, studies of chronic health effects are more difficult than studies of acute effects. Specific reasons have been discussed in the preceding chapters; they include uncertainties in measurements of long-term exposure, the relative rarity of chronic diseases (which strains statistical power), and limitations in our understanding of the biology underlying the gradual evolution of chronic damage. Epidemiologic studies can show whether exposure to a complex pattern of polluted air increases the risk of adverse health effects in human populations, but studies are often limited in their ability to delineate the quantitative relationships between concentrations or sources of specific air pollutants and health. Such delineation requires interpretation of epidemiologic data in conjunction with toxicologic and clinical research. Susceptibility to the effects of air pollution varies widely; studies that focus on sensitive subgroups, necessary in themselves, are an important part of strategies to detect and measure the effects of air pollution in the general population. The sensitive-subgroup approach to increasing the effectiveness of air pollution epidemiology must be furthered by broad-based efforts (toxicology, clinical research, and epidemiology) to clarify the precise nature and degree of sensitivity of such groups as the young, the elderly, those with increased airway reactivity, and those with particular pre-existing diseases. Opportunities for carrying out epidemiologic studies on populations exposed to unusual magnitudes or patterns of air pollution must be specifically sought. By circumventing various methodologic constraints, these studies might provide information that would not otherwise be easily obtained. The opportunities include the use of occupational cohorts exposed to high concentrations, groups living in pristine environments or in highly polluted environments, and groups subjected to marked temporal changes in pollution. Collaboration with researchers in other countries might be necessary. 

CONCLUSIONS AND RECOMMENDATIONS 198 NEW RESEARCH TOOLS AND OPPORTUNITIES Some constraints in air pollution epidemiology could be removed by complementary research to develop and explore the application of new tools for measuring exposure and effect. Such research and development is especially needed in two categories: • New methods for assessing personal exposure and response to air pollution to be selectively incorporated into epidemiologic studies, with attention to the cost-effectiveness of these methods. • Epidemiologic studies designed to determine the characteristics and the predictive value of potentially useful physiologic, biochemical, and morphologic markers of subclinical effects. Personal exposure monitoring and modeling are sometimes useful in epidemiologic research in defining study populations, optimal sample sizes, relationships of surrogate measures to exposures, and the extent of exposure misclassification associated with the use of central monitoring data. Depending on the design of a given study, only a sample of the study population might require such detailed monitoring; various strategies need to be explored and their performance documented. Markers of physiologic, biochemical, and cellular morphologic changes will be increasingly important in air pollution studies. FEV1, a physiologic test of lung function, has been used successfully to measure differences related to air pollution between populations. Serial measurement of FEV1 has also proved to be sensitive and effective in following the growth and decline of lung function in large populations. In adults, a more rapid than normal decline in FEV1 predicts premature death from pulmonary failure. Although FEV1 is a simple and highly reproducible test, its interpretation in terms of organ or cellular pathology is complex and subject to some judgment. Some biochemical indicators of air pollutant exposure or early effects--such as blood lead and carboxyhemoglobin concentrations, urinary mutagens, and indexes of genotoxic damage--have already been successfully applied in population studies. Other biochemical indicators, designed to 

CONCLUSIONS AND RECOMMENDATIONS 199 detect early pathologic processes in the lung, have recently shown promise and require further development and validation. Insights into the pathogenesis of emphysema have been particularly fruitful in opening possibilities for biochemical markers related to the breakdown of connective tissue in the lung. Development of biochemical markers for epidemiologic studies requires particular attention to constraints imposed by the need to study large groups of relatively healthy people. 

CONCLUSIONS AND RECOMMENDATIONS 200 

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• Introduction
• Conclusions
• Article Information

NO 2 indicates nitrogen dioxide; PM 2.5 , particulate matter under 2.5 μm; and WHO, World Health Organization. Shading in panel A represents IQRs.

Results are from model 3, which is adjusted for ethnicity, family psychiatric history, maternal social class, maternal education, house tenure, population density, neighborhood deprivation, social fragmentation, and greenspace. Sample sizes of imputed data sets range from 2952 (adolescence noise pollution and psychotic experiences) to 6154 (pregnancy air pollution and anxiety). NO 2 indicates nitrogen dioxide; OR, odds ratio; and PM 2.5 , particulate matter less than 2.5 μm.

eMethods. Participants, pollution data, covariates, and multiple imputation

eResults. Findings from sensitivity analyses

eDiscussion. Interpretation of sensitivity analyses

eFigure 1. Correlations between NO2, PM2.5, and noise pollution across pregnancy, childhood, and adolescence

eFigure 2. Directed acyclic graph (DAG)

eTable 1. Association of early-life noise pollution exposure with youth mental health problems, treating noise pollution as a categorical variable

eTable 2. Comparison between e-value and covariate point estimates: pregnancy PM2.5 and psychotic experiences

eTable 3. Comparison between e-value and covariate point estimates: adolescent noise pollution and anxiety

eTable 4. Adjusting pollutants for one another: associations of early-life air and noise pollution exposure with youth mental health problems

eTable 5. Restricting to non-movers (~30% of participants): associations of early-life air and noise pollution exposure with youth mental health problems

eTable 6. Complete case analysis: associations of early-life air and noise pollution exposure with youth mental health problems

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Newbury JB , Heron J , Kirkbride JB, et al. Air and Noise Pollution Exposure in Early Life and Mental Health From Adolescence to Young Adulthood. JAMA Netw Open. 2024;7(5):e2412169. doi:10.1001/jamanetworkopen.2024.12169

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Air and Noise Pollution Exposure in Early Life and Mental Health From Adolescence to Young Adulthood

• 1 Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, United Kingdom
• 2 Social, Genetic, and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, United Kingdom
• 3 PsyLife Group, Division of Psychiatry, University College London, London, United Kingdom
• 4 ESRC Centre for Society and Mental Health, King’s College London, London, United Kingdom
• 5 Department of Biostatistics and Health Informatics, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, United Kingdom
• 6 Centre for Implementation Science, Health Service and Population Research Department, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, United Kingdom
• 7 UK Longitudinal Linkage Collaboration, University of Bristol, Bristol, United Kingdom
• 8 MRC Centre for Neuropsychiatric Genetics and Genomics, School of Medicine, Cardiff University, Cardiff, United Kingdom

Question   Is exposure to air and noise pollution in pregnancy, childhood, and adolescence associated with the development of psychotic experiences, depression, and anxiety between 13 and 24 years of age?

Findings   In this longitudinal birth cohort study followed up into adulthood that included 9065 participants with mental health data, higher exposure to fine particulate matter (PM 2.5 ) in pregnancy and childhood was associated with increased psychotic experiences and in pregnancy was associated with higher rates of depression. Higher noise pollution exposure in childhood and adolescence was associated with increased anxiety.

Meaning   These findings build on evidence associating air and noise pollution with mental health, highlighting a role of early-life pollution exposure in youth mental health problems.

Importance   Growing evidence associates air pollution exposure with various psychiatric disorders. However, the importance of early-life (eg, prenatal) air pollution exposure to mental health during youth is poorly understood, and few longitudinal studies have investigated the association of noise pollution with youth mental health.

Objectives   To examine the longitudinal associations of air and noise pollution exposure in pregnancy, childhood, and adolescence with psychotic experiences, depression, and anxiety in youths from ages 13 to 24 years.

Design, Setting, and Participants   This cohort study used data from the Avon Longitudinal Study of Parents and Children, an ongoing longitudinal birth cohort founded in 1991 through 1993 in Southwest England, United Kingdom. The cohort includes over 14 000 infants with due dates between April 1, 1991, and December 31, 1992, who were subsequently followed up into adulthood. Data were analyzed October 29, 2021, to March 11, 2024.

Exposures   A novel linkage (completed in 2020) was performed to link high-resolution (100 m 2 ) estimates of nitrogen dioxide (NO 2 ), fine particulate matter under 2.5 μm (PM 2.5 ), and noise pollution to home addresses from pregnancy to 12 years of age.

Main outcomes and measures   Psychotic experiences, depression, and anxiety were measured at ages 13, 18, and 24 years. Logistic regression models controlled for key individual-, family-, and area-level confounders.

Results   This cohort study included 9065 participants who had any mental health data, of whom (with sample size varying by parameter) 51.4% (4657 of 9051) were female, 19.5% (1544 of 7910) reported psychotic experiences, 11.4% (947 of 8344) reported depression, and 9.7% (811 of 8398) reported anxiety. Mean (SD) age at follow-up was 24.5 (0.8) years. After covariate adjustment, IQR increases (0.72 μg/m 3 ) in PM 2.5 levels during pregnancy (adjusted odds ratio [AOR], 1.11 [95% CI, 1.04-1.19]; P  = .002) and during childhood (AOR, 1.09 [95% CI, 1.00-1.10]; P  = .04) were associated with elevated odds for psychotic experiences. Pregnancy PM 2.5 exposure was also associated with depression (AOR, 1.10 [95% CI, 1.02-1.18]; P  = .01). Higher noise pollution exposure in childhood (AOR, 1.19 [95% CI, 1.03-1.38]; P  = .02) and adolescence (AOR, 1.22 [95% CI, 1.02-1.45]; P  = .03) was associated with elevated odds for anxiety.

Conclusions and Relevance   In this longitudinal cohort study, early-life air and noise pollution exposure were prospectively associated with 3 common mental health problems from adolescence to young adulthood. There was a degree of specificity in terms of pollutant-timing-outcome associations. Interventions to reduce air and noise pollution exposure (eg, clean air zones) could potentially improve population mental health. Replication using quasi-experimental designs is now needed to shed further light on the underlying causes of these associations.

Childhood, adolescence, and early adulthood are critical periods for the development of psychiatric disorders: worldwide, nearly two-thirds of individuals affected become unwell by 25 years of age. 1 Identifying early-life risk factors is a crucial research challenge in developing preventative interventions and improving lifelong mental health trajectories.

Growing evidence suggests that air pollution exposure may be associated with the onset of psychiatric problems, including mood, affective, and psychotic disorders. 2 - 6 Air pollution comprises toxic gases and particulate matter (ie, organic and inorganic solid and liquid aerosols) of mostly anthropogenic origin. 7 Understanding the potential effect of air pollution on mental health is increasingly crucial, given the human and societal cost of poor mental health, 8 the global shift toward urban living, 9 , 10 and the backdrop of emissions-induced climate change. 11 Air pollution could negatively affect mental health via numerous pathways, including by compromising the blood-brain barrier, promoting neuroinflammation and oxidative stress, and directly entering the brain and damaging tissue therein. 12 , 13 However, key research gaps remain. First, the relative importance of early-life exposure, including prenatal exposure, is uncertain. Infants and children are thought to be especially vulnerable to air pollution, 14 , 15 but longitudinal, high-resolution pollution data spanning the early years of human life are scarce. Second, relatively few studies have examined the association of air pollution with youth mental health problems, 16 despite youth being a critical period for intervention. Third, few longitudinal studies have investigated the role of noise pollution in mental health, 17 despite the correlation between noise and air pollution. 18 Finally, studies have often used crude pollution data and lacked adequate controls for potential confounders.

We aimed to advance understanding on this topic by capitalizing on a novel linkage between high-resolution outdoor air and noise pollution data and a cohort of over 14 000 infants born in Southwest England in 1991 through 1993 and followed up into adulthood. We examined the association of air and noise pollution exposure from pregnancy to 12 years of age with mental health problems from ages 13 to 24 years. Based on previous evidence, we focused on psychotic experiences (eg, subclinical hallucinations and delusions), depression, and anxiety. These problems are common 1 , 19 - 21 and increasing 22 among youth and strongly predict future psychopathology, 23 , 24 making them useful and important targets. We hypothesized that participants exposed to higher air and noise pollution would subsequently experience worse mental health.

The Avon Longitudinal Study of Parents and Children (ALSPAC) is a UK birth cohort, 25 - 28 described further in the eMethods in Supplement 1 . Briefly, pregnant women residing in and around the City of Bristol (population approximately 714 000 in 2024) in Southwest England with due dates between April 1, 1991, and December 31, 1992, were approached to take part in the study. The initial number of pregnancies enrolled was 14 551, resulting in 13 988 children alive at 1 year of age. At age 7 years, the initial sample was bolstered with additional eligible cases, resulting in 14 901 infants alive at 1 year of age. The catchment area has a mix of urban, suburban, and rural environments. 29 The study website contains details of all the data and a fully searchable data dictionary and variable search tool. 30 Ethical approval for the study was obtained from the ALSPAC Ethics and Law Committee and the Local Research Ethics Committees. Informed consent for the use of data collected via questionnaires and clinics was obtained from participants following the recommendations of the ALSPAC Ethics and Law Committee at the time. The present study is reported according to the Strengthening the Reporting of Observational Studies in Epidemiology ( STROBE ) reporting guideline. 31

Psychotic experiences were measured at ages 13, 18, and 24 years using a semi-structured interview 32 that consisted of 12 core items about hallucinations, delusions, and thought interference, rated against the Schedule for Clinical Assessment in Neuropsychiatry version 2.0 (SCAN 2.0). 33 Consistent with previous ALSPAC studies, 34 , 35 psychotic experiences were defined such that 0 represented none, and 1 represented suspected or definite. The reporting period at each phase was since the participant’s 12th birthday. At 13 years of age, 13.6% (926 of 6788) of participants reported psychotic experiences, at 18 years of age 9.2% (432 of 4715) reported psychotic experiences, and at 24 years of age, 12.6% (491 of 3888) reported psychotic experiences. We summed psychotic experiences across time points and dichotomized the variable for analyses such that participants received a score of 1 for suspected or definite psychotic experiences if they reported psychotic experiences at any age.

Depression and anxiety were measured at age 13 years via parent-completed Development and Well-being Assessments. 36 Responses were classified into probabilistic bands according to Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition) criteria for major depressive disorder and generalized anxiety disorder, and dichotomized for analysis (bands 0-2, 0; bands 3-5, 1). At ages 18 and 24 years, depression and anxiety were measured using the Clinical Interview Schedule Revised, 37 a self-administered computerized interview that gave International Statistical Classification of Diseases, Tenth Revision , diagnoses of moderate to severe depression and generalized anxiety disorder. The reporting period at each phase was the past month, although a 6-month reporting period was used for anxiety at 13 years of age. At 13 years of age, 5.6% (386 of 6944 of participants) reported depression and 3.6% (254 of 7044) reported anxiety. At 18 years of age, 7.9% (359 of 4560) reported depression and 5.7% (262 of 4560) reported anxiety. At 24 years of age, 7.7% (304 of 3965) reported depression and 9.8% (386 of 3956) reported anxiety. We summed depression and anxiety across time points and dichotomized the variables for analysis such that participants received a score of 1 if they had depression or anxiety at any age.

Air pollutants included nitrogen dioxide (NO 2 ) and fine particulate matter with a diameter smaller than 2.5 μm (PM 2.5 ). Both pollutants have well-established health impacts 10 and more recent associations with psychiatric disorders. 5 These air pollutants were estimated as part of the LifeCycle project 38 using the Effects of Low-Level Air Pollution: A Study in Europe (ELAPSE) model, which is described elsewhere and further in the eMethods in Supplement 1 . 39 Briefly, the ELAPSE model is a hybrid land-use regression model for Europe that derived concentrations of NO 2 and PM 2.5 in 2010. The model produces annualized estimates at 100 m 2 resolution, explaining 59% and 71% of measured spatial variability for NO 2 and PM 2.5 , respectively. 39 Estimates were linked to residential geocodes from pregnancy to age 12 years for participants who had lived in the original ALSPAC catchment area 29 up to 12 years of age and provided permission for geospatial linkage. Linkage was completed in 2020.

Residential noise pollution exposure was also estimated as part of the LifeCycle project 38 based on the UK Government’s Department for Environment, Food and Rural Affairs 2006 road traffic noise map. Data represent an annualized mean of day and night noise pollution, categorized according to low to medium (<55 dB: the European Environment Agency’s threshold 40 ), high (55-60 dB), and very high (>60 dB) noise. eFigure 1 in Supplement 1 shows the correlation between noise pollution, NO 2 , and PM 2.5 across time points.

Potential confounders were informed by the literature and formally selected using a directed acyclic graph (eFigure 2 in Supplement 1 ). We considered individual- and family-level covariates that could be associated with mental health problems and with downward mobility into more polluted neighborhoods. These included ethnicity self-reported by mothers during pregnancy, family psychiatric history, maternal social class, maternal education, and housing tenure. Area-level covariates included population density, neighborhood deprivation, social fragmentation, and greenspace and were time varying, corresponding to the timing of pollution exposure. Covariates are described fully in the eMethods in Supplement 1 and briefly below.

Race and ethnic group was reported by mothers during pregnancy, with specific categories to select including Bangladeshi, Black/African, Black/Caribbean, Black/other, Chinese, Indian, Pakistani, White, and any other ethnic group. Family psychiatric problems were reported by mothers and fathers during pregnancy and defined as the presence of any psychiatric problem affecting the mother, father, or any biological grandparent. Maternal social class based on occupation was reported by mothers during pregnancy. Maternal education was reported by mothers when infants were around 8 months. Home ownership was reported by mothers during pregnancy.

Population density was derived from 1991 and 2001 census data. 35 Area-level deprivation was based on the Index of Multiple Deprivation 2000. 41 Social fragmentation was based on a z-scored sum of census data on residential mobility, marital status, single-person households, and home ownership. 35 Greenspace was assessed based on the Normalized Difference Vegetation Index. 42

Analyses were performed from October 29, 2021, to March 11, 2024, in Stata, version 18.0 (StataCorp LLC). The code can be found at GitHub. 43 The characteristics of the sample with vs without mental health data were described according to percentages, means, and standard deviations. Group differences were explored using χ 2 and t tests. To explore the importance of different exposure periods, we derived exposure estimates for 3 developmental stages, pregnancy, childhood (birth to age 9 years), and adolescence (ages 10-12 years), 44 which were calculated using mean exposure values for NO 2 , PM 2.5 , and noise pollution during these age windows. Given that NO 2 and PM 2.5 had very different absolute ranges, scores were standardized by dividing by the IQR. To aid comparison between air and noise pollution, we treated noise pollution as a continuous variable, assuming a normal distribution underlying the categorical variable. Results treating noise as categorical are reported in eTable 1 in Supplement 1 .

For main analyses, logistic regression was used to examine the associations of NO 2 , PM 2.5 , and noise pollution in pregnancy, childhood, and adolescence with the mental health outcomes. We conducted an unadjusted model (model 1), then adjusted for individual- and family-level covariates (model 2), and then additionally adjusted for area-level covariates (model 3). To better understand the independent associations from different exposure periods, we then adjusted childhood and adolescent exposure for previous exposure (model 4). However, given that the high correlation between pollutants over time (eFigure 1 in Supplement 1 ) could introduce multicollinearity, we interpreted model 4 with caution. To estimate residual confounding, we also calculated E values 45 for models 3 and 4, which indicate the strength of association that an unmeasured confounder would require to nullify associations. All models accounted for potential hierarchy in the data by clustering around the lower layer super output area (containing a mean of about 1500 residents) using the cluster command, which provides robust SEs adjusted for within cluster correlated data. 46 All analyses were conducted following multiple imputation by chained equations, 47 described in the eMethods in Supplement 1 . A 2-sided value of P  < .05 was considered statistically significant.

We conducted 3 sensitivity analyses. First, we analyzed NO 2 , PM 2.5 , and noise pollution simultaneously, to control each for the others and address potential copollutant confounding. Second, we restricted analyses to participants who did not move house from pregnancy to age 12 years (29.8%) to keep pollution levels as consistent as possible over time. Third, we repeated main analyses for individuals with complete data.

The study included 9065 participants (mean [SD] age at follow-up, 24.5 [0.8] years) who had any mental health data, of whom (with sample sizes varying by parameter) 51.4% (4657 of 9051) were female, 48.6% (4394 of 9051) were male, 95.8% (7616 of 7954) were ethnically White, and 4.2% (338 of 7954) were of other ethnicity (which included Bangladeshi, Black African, Black Caribbean, Chinese, Indian, Pakistani, and others; these categories were collapsed into one because numbers in some categories were small enough to increase the risk of identification). In addition, 19.5% (1544 of 7910) reported psychotic experiences, 11.4% (947 of 8344) reported depression, and 9.7% (811 of 8398) reported anxiety ( Table 1 ). Over half of participants (60.8% [4793 of 7886]) had a family psychiatric history; 21.8% (1583 of 7248) had mothers who worked in manual occupations; 15.7% (1274 of 8093) had mothers with degrees; and 81.6% (6670 of 8176) lived in homes owned by their parent (or parents). Mean (SD) population density was 33 (21) persons per hectare, and 19.3% (933 of 4831) of participants lived in the most deprived neighborhoods. The sample with vs without mental health data differed for most variables: participants with mental health data were more likely to be female, be White, have a family psychiatric history, and have more advantaged characteristics across the other variables. These differences should be borne in mind when interpreting the results.

Figure 1 A shows estimated levels of NO 2 and PM 2.5 for the sample, alongside the World Health Organization’s (WHO) 2021 exposure thresholds. 48 Mean (SD) levels of NO 2 (eg, 26.9 [4.2] μg/m 3 in pregnancy vs 21.1 [3.5] μg/m 3 at 12 years of age) and PM 2.5 (eg, 13.3 [0.9] μg/m 3 in pregnancy vs 10.7 [0.8] μg/m 3 at 12 years of age) decreased slightly over time. However, the mean exposure at age 12 years remained above the WHO’s thresholds for both pollutants (NO 2 , 10.0 μg/m 3 ; PM 2.5 , 5.0 μg/m 3 ). Additionally, over two-thirds of participants were exposed to high or very high noise pollution, 40 which changed little over time (eg, 22.7% in pregnancy vs 22.2% at year 12 for high noise pollution) ( Figure 1 B).

Associations of levels of NO 2, PM 2.5 , and noise pollution with psychotic experiences, depression, and anxiety are given in Table 2 , which shows unadjusted and adjusted results alongside E values, and Figure 2 , which shows model 3 results. Before covariate adjustment, IQR (4.47 μg/m 3 ) increases in NO 2 levels during pregnancy were associated with elevated odds for psychotic experiences (odds ratio [OR], 1.08, [95% CI, 1.00-1.17]; P  = .04). However, there was no association after adjusting for area-level covariates. In contrast, following covariate adjustment, IQR (0.72 μg/m 3 ) increases in PM 2.5 during pregnancy (adjusted [A]OR, 1.11 [95% CI, 1.04-1.19]; P  = .002) and childhood (AOR, 1.09 [95% CI, 1.00-1.19]; P  = .04) were associated with elevated odds for psychotic experiences, although for childhood exposure (model 4), there was no association after adjusting for pregnancy exposure. There was no association between noise pollution and psychotic experiences (eg, AOR, 1.04 [95% CI, 0.92-1.18]; P  = .50 during pregnancy).

Following covariate adjustment, IQR increases in PM 2.5 during pregnancy were associated with elevated odds for depression (eg, AOR, 1.10 [95% CI, 1.02-1.18]; P  = .01 during pregnancy). There were no associations between NO 2 (eg, AOR, 1.10 [95% CI, 0.98-1.24]; P  = .10 during pregnancy) or noise pollution (eg, AOR, 1.02 [95% CI, 0.89-1.18]; P  = .74 during pregnancy) and depression.

Before covariate adjustment, IQR increases in NO 2 in pregnancy (OR, 1.14 [95% CI, 1.04-1.26]; P  = .006) and childhood (OR, 1.15 [95% CI, 1.03-1.27]; P  = .009) were associated with elevated odds for anxiety, but associations were attenuated to the null after adjusting for area-level covariates. There were no associations between PM 2.5 exposure during childhood and anxiety (AOR, 1.10 [95% CI, 0.97-1.25]; P = .58 for model 3). In contrast, participants exposed to higher noise pollution in childhood (AOR, 1.19 [95% CI, 1.03-1.38]; P  = .02) and in adolescence (AOR, 1.22 [95% CI, 1.02-1.45]; P  = .03) had elevated odds for anxiety; however, adolescent exposure was attenuated to the null after controlling for pregnancy and childhood exposure (model 4). eTable 1 in Supplement 1 gives results when noise pollution was treated as categorical. This analysis highlighted several dose-response associations, although no difference in model fit was observed compared with the main results.

In eTables 2 and 3 in Supplement 1 , we take as examples the associations of pregnancy PM 2.5 with psychotic experiences and adolescent noise pollution with anxiety from model 3 and compare the E values to the associations from included covariates. The E value ORs were 1.46 (lower confidence limit, 1.24) for pregnancy PM 2.5 with psychotic experiences and 1.74 (lower confidence limit, 1.16) for adolescent noise pollution with anxiety. These E value ORs were larger in magnitude than the ORs for associations of the covariates with the exposures and outcomes, indicating that an unmeasured confounder would require a relatively strong confounding influence to nullify associations.

Results from sensitivity analyses are described in the eResults in Supplement 1 , presented in eTables 4 to 6 in Supplement 1 , and addressed in the eDiscussion in Supplement 1 . Briefly, point estimates were generally similar after adjusting pollutants for each other, similar (and often higher) for participants who did not move house, and similar for complete cases, although CIs were often less precise.

In this longitudinal birth cohort study with a follow-up of approximately 25 years, participants exposed to higher PM 2.5 during pregnancy and childhood subsequently experienced more psychotic experiences and (for pregnancy exposure only) depression. In contrast, higher noise pollution in childhood and adolescence were associated subsequently with more anxiety. These associations were not explained by numerous potential individual-, family-, and area-level confounders.

Our findings suggest an important role of early-life (including prenatal) exposure to air pollution in the development of youth mental health problems. Early-life exposure could be detrimental to mental health given the extensive brain development and epigenetic processes that occur in utero and during infancy. 13 , 15 , 49 , 50 Air pollution exposure could also lead to restricted fetal growth 51 and preterm birth, 52 which are both risk factors for psychopathology. Notably, the point estimate for pregnancy PM 2.5 and depression (10% elevated odds for every 0.72 μg/m 3 increase) was considerably greater than a previous meta-analytic estimate based on exposure in adulthood (10% elevated odds for every 10 μg/m 3 increase). 2 These contrasting findings are in keeping with a particularly detrimental role of early-life air pollution exposure. However, our findings could also have arisen if early-life exposure data provide a proxy for cumulative exposure over a longer period, given that families often settle when children are young.

For noise pollution, evidence was strongest for childhood and adolescent exposure. Childhood and adolescent noise pollution exposure could increase anxiety by increasing stress and disrupting sleep, with high noise potentially leading to chronic physiological arousal and disruption to endocrinology. 53 Noise pollution could also impact cognition, 54 which could increase anxiety by impacting concentration during school years. It was interesting that noise pollution was associated with anxiety but not with psychotic experiences or depression. However, our measure of noise pollution estimated only decibels (ie, intensity) from road sources. Other qualities of noise, such as pitch, could be relevant to mental health.

We acknowledge several limitations. First, the causality of the findings is uncertain given that data were observational. Despite comprehensive covariate adjustment, residual confounding is inevitable given imperfect selection and measurement of covariates. The relatively large E values strengthened our confidence in the findings, but future studies should consider other methods to address confounding, such as quasi-experimental designs. Second, ALSPAC families are more affluent and less diverse than the UK population. 55 The extent to which our findings generalize to other populations and locations is uncertain. Our findings likely generalize to cities and surrounds in other high-income countries, but may be less generalizable to urban settings in lower-income countries, which can have more extreme pollution concentrations. 56 Third, modeled pollution data are subject to various sources of measurement error, 39 particularly Berkson-like error whereby estimates are smoother (less variable) than reality, leading to less precise, although unbiased, exposure-outcome estimates. 57 , 58 For instance, the 100 m 2 resolution, although an improvement over many previous studies, 59 - 61 would have masked hyperlocal variation (eg, differences between participants living on adjacent streets), to which NO 2 is especially prone due to its short decay function. 62 Additionally, the model estimated residential exposure, which would have masked variation due to behavior and time spent away from home. Finer-resolution data, including personal exposure estimates, would enable more precise exposure-outcome estimates, particularly for NO 2 . Fourth, we could not apply life-course models to investigate sensitive periods vs cumulative effects, as there was limited within-person variation in exposure over time. Larger data sets (eg, national registries) and quasi-experimental designs would be required to further tease out this question.

The results of this cohort study provide novel evidence that early-life exposure to particulate matter is prospectively associated with the development of psychotic experiences and depression in youth. This study, which is among only a handful of longitudinal studies to investigate the association between noise pollution and mental health, also finds an association with anxiety. The findings suggest a degree of specificity in terms of pollutant-timing-outcome pathways. The opportunity for intervention is potentially enormous. However, although our this study addressed various biases affecting observational research, the causality of the findings remains uncertain. There is now a pressing need for further longitudinal research using more precise measures of air and noise pollution and for replication using quasi-experimental designs.

Accepted for Publication: March 15, 2023.

Published: May 28, 2024. doi:10.1001/jamanetworkopen.2024.12169

Open Access: This is an open access article distributed under the terms of the CC-BY License . © 2024 Newbury JB et al. JAMA Network Open .

Corresponding Author: Joanne B. Newbury, PhD, Population Health Sciences, Bristol Medical School, Oakfield House, Bristol, BS8 2BN, United Kingdom ( [email protected] ).

Author Contributions: Dr Newbury had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Newbury, Kirkbride, Fisher, Bakolis.

Acquisition, analysis, or interpretation of data: Newbury, Heron, Kirkbride, Boyd, Thomas, Zammit.

Drafting of the manuscript: Newbury.

Critical review of the manuscript for important intellectual content: All authors.

Statistical analysis: Newbury, Heron, Bakolis.

Obtained funding: Newbury, Zammit.

Administrative, technical, or material support: Boyd, Thomas.

Supervision: Heron, Kirkbride, Fisher, Bakolis, Zammit.

Conflict of Interest Disclosures: Prof Fisher reported receiving grants from the Economic and Social Research Council (ESRC) during the conduct of the study. Dr Heron and Prof Zammit are supported by a grant from the National Institute for Health and Care Research (NIHR) Biomedical Research Centre. Prof Fisher is supported by the ESRC Centre for Society and Mental Health at King’s College London. Dr Bakolis is supported in part by the NIHR Biomedical Research Centre at South London and Maudsley National Health Service (NHS) Foundation Trust and King’s College London and by the NIHR Applied Research Collaboration South London (NIHR ARC South London) at King’s College Hospital NHS Foundation Trust. Messrs Boyd and Thomas are funded by the UK Medical Research Council (MRC) and ESRC to develop centralized record linkage services via the UK Longitudinal Linkage Collaboration and by Health Data Research UK to support the development of social and environmental epidemiology in longitudinal studies. No other disclosures were reported.

Funding/Support: The UK MRC and Wellcome Trust (grant 217065/Z/19/Z) and the University of Bristol provide core support for the Avon Longitudinal Study of Parents and Children (ALSPAC). This research was funded in whole, or in part, by grant 218632/Z/19/Z from the Wellcome Trust. This research was specifically funded by grants from the UK MRC to collect data on psychotic experiences, depression, and anxiety (MR/M006727/1 and G0701503/85179 to Prof Zammit); and a grant from the Natural Environment Research Council to facilitate linkage to geospatial and natural environment data (R8/H12/83/NE/P01830/1 to Mr Boyd). Dr Newbury is funded by Sir Henry Wellcome Postdoctoral Fellowship 218632/Z/19/Z from the Wellcome Trust and grant COV19/200057 from the British Academy.

Role of the Funder/Sponsor: The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Disclaimer: This publication is the work of the authors, and they serve as guarantors for the contents of this paper. The views expressed are those of the authors and not necessarily those of the ESRC or King’s College London.

Data Sharing Statement: See Supplement 2 .

Additional Contributions: We are extremely grateful to all the families who took part in this study; the midwives for their help in recruiting them; and the whole ALSPAC team, which includes interviewers, computer and laboratory technicians, clerical workers, research scientists, volunteers, managers, receptionists, and nurses. We are also extremely grateful to ISGlobal, Barcelona, for conducting the LifeCycle project and generating the air and noise pollution data.

Additional Information: A comprehensive list of grant funding is available on the ALSPAC website ( http://www.bristol.ac.uk/alspac/external/documents/grant-acknowledgments.pdf ).

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