Air pollution

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

There's nothing quite like opening the door and breathing fresh, clean, air—but how clean is the air you're breathing right now? Unless you're a scientist with a chemistry lab at your fingertips, there's no real way of knowing. The gases you're sucking up through your nose could be slowly killing you: according to the World Health Organization, around 4.2 million people die prematurely from the effects of polluted, outdoor air every single year, while a further 3.8 million die due to dirty indoor air. Air pollution is a huge problem—and not just for people living in smog-choked cities: through such things as global warming and damage to the ozone layer, it has the potential to affect us all. So what exactly causes this major environmental issue and what can we do about it? Let's take a closer look!

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 lets our living planet breathe—it's the mixture of gases that fills the atmosphere, giving life to the plants and animals that make Earth such a vibrant place. Broadly speaking, air is almost entirely made up of two gases (78 percent nitrogen and 21 percent oxygen), with a few other gases (such as carbon dioxide and argon) present in much smaller quantities. [1] We can breathe ordinary air all day long with no ill effects, so let's use that simple fact to define air pollution, something like this:

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).

As with water pollution and land contamination, it's the quantity (or concentration) of a chemical in the air that makes the difference between "harmless" and "pollution." Carbon dioxide (CO2), for example, is present in the air around you at a typical concentration of less than 0.05 percent and breathing it in usually does no harm (you breathe it out all day long); but air with an extremely high concentration of carbon dioxide (say, 5–10 percent) is toxic and could kill you in a matter of minutes. [2] Since Earth's atmosphere is very turbulent—many of us live in windy countries—air pollution will often disperse relatively quickly. In less enlightened times, factory operators thought that if they built really high smokestacks, the wind would simply blow their smoke away, diluting and dispersing it so it wouldn't be a problem. The only trouble was, Earth is a much smaller place than we think and pollution doesn't always disappear so conveniently. [3]

Natural air pollution

When we think of pollution, we tend to think it's a problem that humans cause through ignorance or stupidity—and that's certainly true, some of the time. However, it's important to remember that some kinds of air pollution are produced naturally. Forest fires, erupting volcanoes, and gases released from radioactive decay of rocks inside Earth are just three examples of natural air pollution that can have hugely disruptive effects on people and the planet.

Forest fires (which often start naturally) can produce huge swathes of smoke that drift for miles over neighboring cities, countries, or continents. Giant volcanic eruptions can spew so much dust into the atmosphere that they block out significant amounts of sunlight and cause the entire planet to cool down for a year or more. [4] Radioactive rocks can release a gas called radon when they decay, which can build up in the basements of buildings with serious effects on people's health (each year, around 21,000 people die of lung cancer, due to radon gas, in the United States).

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.

All these things are examples of serious air pollution that happen without any help from humans; although we can adapt to natural air pollution, and try to reduce the disruption it causes, we can never stop it happening completely. For the rest of this article, we'll consider only the "unnatural" types of pollution: the problems that people cause—and the ones we can solve.

What are the causes of air pollution?

Anything people do that involves burning things (combustion), using household or industrial chemicals (substances that cause chemical reactions and may release toxic gases in the process), or producing large amounts of dust has the potential to cause air pollution. Step back a century or two and the cause of most air pollution was easy to identify: filthy factories and power plants, driving the Industrial Revolution. Today, better technology, tighter air pollution laws, greater environmental awareness, and determined campaigns mounted by local communities make it far harder—though by no means impossible—for factories to pollute in post-industrial nations such as the United States and Britain. But this type of "old-school" pollution remains a major problem in rapidly industrializing nations such as China and India.

Where, then, does modern air pollution come from? In developed countries such as the United States and the UK, by far the biggest culprit today is traffic, though power plants and factories continue to make an important contribution. Before we start laying the blame for air pollution, let's remember one very important thing: most of us drive (or travel in) cars, use electricity, and buy goods made in factories. If we're pointing fingers, ultimately we're going to have to point them at ourselves.

Now let's look a bit more closely at these three key sources of air pollution.

Traffic

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).

There are over one billion cars on the road today (one for every two people in rich countries such as the United States) and there will be two billion by 2040. Despite the fast growing interest in electric cars, virtually all of the world's vehicles are currently powered by gasoline and diesel engines that burn petroleum to release energy. Petroleum is made up of hydrocarbons (large molecules built from hydrogen and carbon) and, in theory, burning them fully with enough oxygen should produce nothing worse than carbon dioxide and water. In practice, fuels aren't pure hydrocarbons (they contain extra chemicals called "additives") and engines don't burn them cleanly. As a result, exhausts from engines contain all kinds of pollution, notably particulates (soot of various sizes), carbon monoxide (CO), nitrogen oxides (NOx), volatile organic compounds (VOCs), and lead—and indirectly produce ozone. Mix this noxious cocktail together and energize it with sunlight and you get the sometimes brownish, sometimes blueish fog of pollution we call smog, which can hang over cities for days on end.

Vehicles don't release pollution only from their tailpipes. Brake and tire wear and tear, the slow rubbing away of the road surface as tires rumble over it, and stirring up of the dust and debris on top of it also release significant amounts of PM10 and PM2.5 particulates into the air. [15]

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Power plants

Renewable energy sources such as solar panels and wind turbines are helping us generate a bigger proportion of our power every year, but the overwhelming majority of electricity (about two thirds in the United States) is still produced by burning fossil fuels such as coal, gas, and oil, mostly in conventional power plants. Just like car engines, power plants should theoretically produce nothing worse than carbon dioxide and water; in practice, fuels are dirty and they don't burn cleanly, so power plants produce a range of air pollutants, notably sulfur dioxide, nitrogen oxides, and particulates. (They also release huge amounts of carbon dioxide, a key cause of global warming and climate change when it rises and accumulates in the atmosphere. We discuss this a bit more down below.)

Industrial plants and factories

Plants that produce the goods we all rely on often release small but significant quantities of pollution into the air. Industrial plants that produce metals such as aluminum and steel, refine petroleum, produce cement, synthesize plastic, or make other chemicals are among those that can produce harmful air pollution. Most plants that pollute release small amounts of pollution continually over a long period of time, though the effects can be cumulative (gradually building up). Sometimes industrial plants release huge of amounts of air pollution accidentally in a very short space of time. One notable case happened in Bhopal, India in December 1984, when a large chemical plant run by the Union Carbide company released a poisonous gas (methyl isocyanate) that hung over the local area, killing around 3000 people and injuring thousands more. (Wikipedia's article on the Bhopal Disaster gives a comprehensive account of what happened.)

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).

Other causes of air pollution

Although traffic, power plants, and industrial and chemical plants produce the majority of Earth's outdoor air pollution, many other factors contribute to the problem. The causes of indoor air pollution are very different. In many parts of the world, people still rely on burning solid fuels (such as wood, coal, and animal dung) for their cooking and heating, and that produces indoor air pollution that can seriously harm their health (cleaner cookstoves, including solar cookers, are the solution to that problem). But even in richer countries, the fashion for sitting cosily round wood-burning stoves has spawned both a "new" form of air pollution—and a throwback to an age when people didn't know any better. (In the UK, for example, woodburners produce 2.4 times more PM2.5 particulate pollution than traffic, while in Sydney, Australia they cause three quarters of all particulate pollution. [21]) In some areas, garbage is incinerated instead of being recycled or landfilled and that can also produce significant air pollution unless the incinerators are properly designed to operate at a high enough temperature (even then, there is a toxic residue left behind that must be disposed of somehow).

What effects does air pollution have?

Air pollution can harm the health of people and animals, damage crops or stop them growing properly, and make our world unpleasant and unattractive in a variety of other ways.

Human health

We know air pollution is a bad thing without even thinking about it. Have you ever coughed when a truck drove past belching out its sooty exhaust? Instinctively, you cough to clear your lungs and protect your body and you might even cover your face with your handkerchief or sleeve to filter the air until it feels safe to breathe deeply again. You don't have to be told that pollution like this might harm your health to want to steer clear of it: your body takes action automatically. The only trouble is, we can't always see or smell air pollution, tell when it's affecting us, or know how it might harm us days, months, or even years in the future.

It's no big surprise that air pollution is linked to respiratory (breathing) problems such as asthma and pneumonia. But medical research has now connected it to a huge range of other health problems, including heart disease, strokes, high blood pressure, diabetes, dementia, fertility problems, various cancers, cataracts, and all sorts of birth-related problems (including miscarriages and low-birth weight). [16]

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.

Sometimes the connection between air pollution and human health is obvious, as in the Bhopal Disaster. Another notable incident happened in London, England in 1952 when thick, deadly pollution known as the Great Smog, caused by people burning coal in home fires and coal-fired power plants, killed over 4000 people (the official death toll at the time, though later estimates suggest many more). [17] Other times, it's much more difficult to make the link. Rough estimates suggest perhaps 10–20 percent of certain cancers are caused by air pollution of one kind or another, but cancers can take a long time to develop and many other things can cause them too. Proving a direct link with a particular kind of air pollution (say, a garbage incinerator in your community or a neighbor who persistently burns plastic on garden bonfires) is very difficult.

According to the World Health Organization (WHO), air pollution is one of the world's biggest killers: outdoor (ambient) pollution causes around four million people to die prematurely each year, while indoor (household) pollution (mainly from fuel burning) kills another 3.8 million. Many of these deaths happen in less-developed or developing countries (over 2.3 million in India and 1.8 million in China alone), but wealthier industrial nations suffer too: in the United States, for example, around 200,000 people a year are estimated to die early because of air pollution. Imagine how much media coverage there would be if several million people (that's roughly the population of Houston, Texas or the West Midlands conurbation in England) were killed in a terrorist incident or an earthquake. Because air pollution kills quietly and relentlessly, and its finger is hard to detect on the trigger, people barely seem to notice—or care.

Deaths aren't the only human consequence of air pollution. For every person who dies, hundreds or thousands more suffer breathing problems such as asthma and bronchitis. Workers exposed to high levels of dust sometimes suffer years of misery before dying from illnesses such as silicosis. And though we naturally expect air pollution to cause respiratory diseases, it's crucial to note that its effects are very much more widespread. According to a recent review by Professor Dean Schraufnagel of the University of Illinois at Chicago, and a team of medical experts from around the world: "Although air pollution is well known to be harmful to the lung and airways, it can also damage most other organ systems of the body."

Agricultural effects

Farming is as much of an art as a science; crops can thrive—or fail—for all sorts of reasons. One of the things that characterized the 20th century was the huge growth in industrial agriculture—using fertilizers, pesticides, and so on to increase crop yields and feed the world's ever-growing population. These aren't the only chemicals that crops are exposed to, however. We know that air pollution (in common with water pollution) can seriously affect the growth of plants. At one end of the spectrum, it's easy to find chemical residues (everything from toxic heavy metals such as lead to cocktails of brake fluids and other chemicals) in plants that grow alongside highways. At the opposite extreme, the huge increase in atmospheric carbon dioxide now causing global warming and climate change is expected to have a major impact on the world's agriculture (reducing crop yields in some places but potentially increasing yields elsewhere). Somewhere in between those local and global impacts, air pollutants such as ozone can have a dramatic, regional effect on crop yields.

Other effects

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.

Wander the streets of a big city and you'll notice quite quickly how dirty the buildings look, even in areas where there are no factories or power plants. Exhaust fumes from traffic are generally to blame. Apart from blackening buildings with soot, they also contribute to acid rain (see below) that can wear away stonework in a matter of years or decades. If you look through UNESCO's list of World Heritage Sites, you'll find air pollution is a major menace that affects some of the world's most prizes historic places, from the Taj Mahal (India) and the Acropolis (Greece) to the Colosseum (Rome) and the Leshan Buddha (China).

How air pollution works on different scales

Air pollution can happen on every scale, from the local to the global. Sometimes the effects are immediate and happen very near to the thing that caused them; but they can also happen days, months, or even years later—and in other cities, countries, or continents.

Local air pollution

Have you ever sat on a train with someone who suddenly decided to start cleaning or varnishing their nails? Acetone (a solvent in nail varnish remover) is a VOC (volatile organic compound), so it evaporates and spreads very quickly, rapidly getting up the nose of anyone sitting nearby. Open a can of gloss paint in your home and start painting a door or window and your house will very quickly fill with a noxious chemical stench—VOCs again! Grill some toast too long and you'll set the bread on fire, filling your kitchen with clouds of soot (particulates) and possibly setting off a smoke alarm or carbon monoxide detector. These are three everyday examples of how air pollution can work on a very local scale: the causes and the effects are close together in both space and time. Localized air pollution like this is the easiest kind to tackle.

Neighborhood air pollution

How clean your air is depends on where you live: air is generally far cleaner in rural than in urban areas, for example, where factories, chemical plants, and power plants are more likely to be located and traffic levels are much higher. Exactly how clean your neighborhood is can also depend critically on the weather, especially if you live somewhere prone to temperature inversions and smog. Neighborhood air pollution problems are often best tackled through local community campaigns.

Regional air pollution

Tall smokestacks designed to disperse pollution don't always have that effect. If the wind generally blows in the same direction, the pollution can be systematically deposited on another city, region, or country downwind. Sometimes air pollution is carried back down to Earth as contaminated rain or snow, which dissolves in watercourses or oceans causing what's known as atmospheric deposition. In other words, the air pollution becomes water pollution. According to the US Environmental Protection Agency (EPA): "The air is a major source of chemicals affecting the health of the Great Lakes. Certain persistent air toxics may contribute not only to atmospheric pollution but to water pollution. These toxics can bioaccumulate in the food web [and] may endanger the environment, affecting the health of humans and wildlife." Acid rain (see box below) is the best known example of atmospheric deposition.

It's often said that pollution knows no boundaries—and that's particularly true of air pollution, which can easily blow from one country or continent where it's produced and cause a problem for someone else. Air pollution that travels like this, from country to country, is called transboundary pollution; acid rain is also an example of this and so is radioactive fallout (the contaminated dust that falls to Earth after a nuclear explosion). When the Chernobyl nuclear power plant exploded in the Ukraine in 1986, wind dispersed the air pollution it produced relatively quickly—but only by blowing a cloud of toxic radioactive gas over much of Europe and causing long-lasting problems in a number of other countries (70 percent of the fallout landed on neighboring Belarus).

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

Photo: Global air pollution: The purple area is the huge hole in the ozone layer over Antarctica caused by CFC chemicals in aerosol sprays and refrigerants. Picture courtesy of NASA on the Commons.

Global warming is a really dramatic effect of air pollution produced by humans, but that doesn't mean it's an insoluble problem. People have already managed to solve another huge air pollution problem that affected the whole world: the damage to a part of the atmosphere called the ozone layer. At ground level, ozone is an air pollutant—but the ozone that exists in the stratosphere (high up in the atmosphere), is exactly the opposite: it's a perfectly natural chemical that protects us like sunscreen, blocking out some of the Sun's harmful ultraviolet radiation. During the 20th century, people started using large quantities of chemicals called chlorofluorocarbons (CFCs), because they worked very well as cooling chemicals in refrigerators and propellant gases in aerosol cans (propellants are the gases that help to fire out air freshener, hair spray, or whatever else the can contains). In 1974, scientists Mario Molina and Sherwood Rowland suggested that chlorofluorocarbons attacked and destroyed the ozone layer, producing holes that would allow dangerous ultraviolet light to stream through. In the 1980s, huge "ozone holes" started to appear over Antarctica, prompting many countries to unite and sign an international agreement called the Montreal Protocol, which rapidly phased out the use of CFCs. As a result, the ozone layer—though still damaged—is expected to recover by around 2060–2080.

How can we solve the problem of air pollution?

As we discovered in the last section, air pollution means different problems at different scales—in other words, it's not one single problem but many different ones. Solving a problem like passive smoking (how one person's cigarette smoke can harm other people's health) is very different to tackling a problem like global warming, though both involve air pollution and they do have some things in common (both problems, for example, require us to think about how our behavior can affect other people in the short and long term and to act more considerately). Generally, air pollution is tackled by a mixture of technological solutions, laws and regulations, and changes in people's behavior.

Technological solutions

It's very easy to criticize power plants, factories, and vehicles that belch polluting gases into the atmosphere, but virtually all of us rely on these things—ultimately, we are the people polluting. Solving air pollution is also a challenge because many people have a big investment in the status quo (carrying on with the world much as it is today). For example, it's easier for car makers to keep on making gasoline engines than to develop electric cars or ones powered by fuel cells that produce less pollution. The world has thousands of coal-fired power plants and hundreds of nuclear power stations and, again, it's easier to keep those going than to create an entirely new power system based on solar panels, wind turbines, and other forms of renewable energy (though that is happening steadily). Growing awareness of problems such as air pollution and global warming is slowly forcing a shift to cleaner technologies, but the world remains firmly locked in its old, polluting ways.

Let's be optimistic, though. Just as technology has caused the problem of air pollution, so it can provide solutions. Cars with conventional gasoline engines are now routinely fitted with catalytic converters that remove some (though not all) of the pollutants from the exhaust gases. Power plants are fitted with electrostatic smoke precipitators that use static electricity to pull dirt and soot from the gases that drift up smokestacks; in time, it's likely that many older power plants will also be retro-fitted with carbon capture systems that trap carbon dioxide to help reduce global warming. On a much smaller scale, environmentally friendly people who want to ventilate their homes without opening windows and wasting energy can install heat-recovery ventilation systems, which use the heat energy locked in outgoing waste air to warm fresh incoming air. Technologies like this can help us live smarter—to go about our lives in much the same way with far less impact on the planet.

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).

Laws and regulations

By itself, technology is as likely to harm the environment as to help it. That's why laws and regulations have been such an important part of tackling the problem of pollution. Many once-polluted cities now have relatively clean air and water, largely thanks to anti-pollution laws introduced during the mid-20th century. In England, following the 1952 smog tragedy that killed thousands in the capital city of London, the government introduced its Clean Air Act of 1956, which restricted how and where coal could be burned and where furnaces could be sited, and forced people to build smokestacks higher to disperse pollution. [19] In the United States, a series of Clean Air Acts were passed between the 1960s and 1990s. The 1990 Pollution Prevention Act went even further, shifting the emphasis from cleaning up pollution to preventing it ever happening in the first place. [20]

National laws are of little help in tackling transboundary pollution (when air pollution from one country affects neighboring countries or continents), but that doesn't mean the law is useless in such cases. The creation of the European Union (now comprising around 30 different countries) has led to many Europe-wide environmental acts, called directives. These force the member countries to introduce their own, broadly similar, national environmental laws that ultimately cover the entire European region. For example, the 1976 European Bathing Water Directive tried to enforce minimum standards of water quality for beaches and coastal areas across Europe to reduce pollution from sewage disposal, while the 1996 European Directive on Integrated Pollution Prevention and Control (IPPC) (overhauled in 2008) attempted to limit air and water pollution from industry. Other successful international laws include the Convention on Long-Range Transboundary Air Pollution (1979), which has helped to reduce sulfur dioxide emissions from power plants and, of course, the Montreal Protocol, which successfully brought 196 countries together to target ozone depletion. Unfortunately, attempts to control global warming through international laws and agreements have so far proved less successful.

Raising awareness and changing behavior

Clean technologies can tackle dirty technologies, and laws can make polluters clean up their act—but none of this would happen without people being aware of pollution and its damaging effects. Sometimes it takes horrific tragedies (like the 1952 smog episode in London or the Chernobyl catastrophe) to prompt action. Often, we pollute the environment without even realizing it: how many people know that taking a shower or ironing a shirt can release indoor air pollution from hot water that they immediately breathe in, for example? Helping people to understand the causes and effects of pollution and what they can do to tackle the issue is very important—that's why I'm writing these words now and probably why you're reading them. Air pollution isn't someone else's problem: all of us help to cause it and we can all help to clean it up. Starting now!

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On this site

You might like some of these other articles on Explain that Stuff covering related topics:

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

Books

Introductory books

• 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.

For younger students

• 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.

For older students

• Understanding Environmental Pollution by Marquita K. Hill. Cambridge University Press, 2020. This wide-ranging introduction covers air and water pollution, and related issues.
• Fundamentals of Air Pollution by Daniel Vallero. Addison-Wesley, 2014. Another huge (1000-page) guide suitable for undergraduates and older students.
• Introduction to Air Pollution Science: A Public Health Perspective by Robert F. Phalen and Robert N. Phalen. Jones & Bartlett Publishers, 2012. There is more of a medical emphasis in this book, which starts with a basic run-through of pollution science and history before moving on to public health topics such as toxicology, epidemiology, risk assessment, and ethics.
• Air Pollution by Abhishek Tiwary and Jeremy Colls. Routledge/Taylor and Francis, 2017. A very detailed (500-page) guide suitable for older students and general readers.
• Air Pollution: Its Origin and Control by Kenneth Wark, Cecil Francis Warner, and Wayne T. Davis. Addison-Wesley, 1998. A huge classic guide to pollution, now in its third edition.

Reports, statistics, and data

• 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.

News articles

There are constant news articles about air pollution and it's only possible to list a small, representative selection here. You can find the newest stories by following the "latest articles" links to the running archives maintained by some of the better newspapers:

Latest articles

• The New York Times Topics: Air Pollution
• The Guardian: Pollution
• Wired: Pollution

Older articles

• '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.

Journal articles

There are literally thousands of scientific articles about air pollution. These three are an excellent starting point if you're researching the health impacts of pollution:

• 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

References

1. ↑   NASA Earth Fact Sheet, 02 April 2020.
2. ↑   NASA Earth Fact Sheet, 02 April 2020, gives the concentration of carbon dioxide as 410 parts per million or 0.04 percent. According to the US CDC, "100,000 ppm is the atmospheric concentration immediately dangerous to life" (roughly 250 times greater).
3. ↑   For a review of the effectiveness of smokestacks, see Information on Tall Smokestacks and Their Contribution to Interstate Transport of Air Pollution, US Government Accountability Office, May 11, 2011.
4. ↑   The most famous eruption in history, Krakatoa, cooled the world by about 0.5°C for five years from 1883, while a less well known but bigger eruption at Mount Tambura in 1815 is believed to have produced a 3–5°C cooling. See Volcanic Eruption That Changed World Marks 200th Anniversary by Jane Lee, National Geographical, 2015.
5. ↑   Sulphur dioxide: health effects and incident management, Public Health England, 2016.
6. ↑   For examples of how ship operators are working to cut sulphur dioxide, see: Sulphur 2020—cutting sulphur oxide emissions, International Maritime Organization, 2020.
7. ↑   Carbon Monoxide's Impact on Indoor Air Quality, US Environmental Protection Agency, undated, retrieved June 2020.
8. ↑   Carbon Dioxide, NASA Vital Signs, May 2020.
9. ↑   What are Nitrogen Oxides?, ToxTown, US National Library of Medicine, May 31, 2017. [Archived via the Wayback Machine]
10. ↑   What are Volatile Organic Compounds (VOCs)?, ToxTown, US National Library of Medicine, May 31, 2017. [Archived via the Wayback Machine]
11. ↑   Health Effects of Fine Particulate Air Pollution: Lines That Connect by C Arden Pope and Douglas W Dockery, J Air Waste Manag Assoc, 2006.
12. ↑   Ground-level Ozone Pollution, US Environmental Protection Agency, January 9, 2020.
13. ↑   The Atmosphere: Tracking the Ongoing Recovery of Earth's Ozone Hole by Alan Buis, NASA Jet Propulsion Laboratory.
14. ↑   Lead poisoning and health, World Health Organization, 23 August 2019.
15. ↑   For a comprehensive look at non-exhaust emissions, see for example Non-Exhaust Emissions by F. Amato (ed). Academic Press, 2018. For a quick review of why they matter, see London should lead in showing electric cars will not tackle air pollution by Frank Kelly, The Guardian, 4 August 2017.
16. ↑   For a comprehensive overview, try these three papers: 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; and Ambient and household air pollution: complex triggers of disease by Stephen A. Farmer et al, Am J Physiol Heart Circ Physiol, 2014.
17. ↑   There's a good overview of the Great London Smog in Chapter 3 of The Invisible Killer by Gary Fuller, Melville House, 2018, p.39.
18. ↑   The most comprehensive account is still The Dirty Man of Europe by Chris Rose, Simon & Schuster, 1990.
19. ↑   For a good review of the importance of the 1956 act, see The Clean Air Act after 50 years by Professor Peter Brimblecombe, Weather, 16 January 2007.
20. ↑   For a review of the effectiveness of US clean-air legislation, see Progress Cleaning the Air and Improving People's Health, US EPA, 2019 and Air pollution success stories in the United States: The value of long-term observations by Timothy Sullivan et al, Environmental Science & Policy, Volume 84, June 2018, Pages 69–73.
21. ↑   Air pollution in UK: the public health problem that won’t go away by Dr Dorothy L Robinson, British Medical Journal, May 22, 2015; Wood fire heaters: the hidden killer by Heath Gilmore, Sydney Morning Herald, June 28, 2014. There's a good discussion in Chapter 11 of The Invisible Killer by Gary Fuller, Melville House, 2018, p.151 ("Wood burning—the most natural way to heat my home?").
22. ↑ Chart last revised in November 2022 using the latest city data in the 2016 and 2022 World Health Organization Air Quality Database. For any given city, in the 2022 database, the latest available pollution data might have been recorded in 2020, 2019 or earlier, while in the 2016 database, it might have come from 2016, 2014, or earlier—but I've always used the latest data for a given city. Note that the WHO's PM2.5 guideline was halved from 10μg per cubic meter to 5μg per cubic meter in September 2021. For all the current guidelines, see the WHO's Ambient (outdoor) air pollution fact sheet.