Health Effects of Air Pollution

We examine the respiratory and other health impacts of indoor and outdoor air pollution. We explain the health problems associated with particulate matter, aerosols, black carbon, nitrogen dioxide, ground-level ozone and sulfur dioxide. We ask: which are the most dangerous pollutants? Whose health is most at risk from air pollution? How many Americans die from ambient air pollution each year? And we explain why World Health Organization estimates of deaths from pollution could be way too low.
Heavy air pollution in China
Heavy air pollution in Ningbo, Zhejiang Province, China Photo: Siyuwj/Flickr (CC BY-SA 2.0)

90 Percent of Air Pollution Deaths Occur in Developing Countries

The health impacts of air pollution (outdoor and indoor) are becoming a major concern. The World Health Organization (WHO) calculates that polluted air kills 8 million people annually, and recent independent evidence suggests this may be a serious underestimate.

In any event, by improving air quality, countries can reduce the incidence of a wide range of serious diseases, including heart disease, stroke, lung cancer and other acute respiratory conditions, including asthma.

What’s more, the primary cause of air pollution is the burning of fossil fuels, which also happens to be the main driver of climate change, which is intensifying rapidly. So, by reducing airborne pollution we also help to tackle our climate crisis and save the planet.

Unfortunately, most countries suffering from dirty air are relatively poor by Western standards. For example, 9 out of 10 of all pollution-related deaths occurred in low- and middle-income countries, such as India, China and other countries in sub-Saharan Africa. Countries least affected include western and northern Europe.

In the U.S., around 40 percent of the population – 134 million people — are at risk of disease and premature death due to the unhealthy state of air quality, according to American Lung Association estimates.

But airborne pollution is a global, not a national problem. Pollutants like aerosols and particulate matter can be blown halfway across the world. For example, soot and ash from the Australian bushfires 2019-2020 crossed the Pacific in less than 7 days to reach South America in early 2020. Arctic fires in the same year wafted across Russia and Eastern Europe.

Meantime, almost one third of the air over San Francisco and Los Angeles can be traced directly to Asia, and it contains 75 percent of the black carbon pollution that reaches the West Coast. 1

What Are the Most Dangerous Forms of Air Pollution?

The pollutants of most concern to medical experts are: particulate matter (PM), including black carbon; ground level ozone (O3); sulphur dioxide (SO2) and nitrogen dioxide (NO2). 2 These pollutants cause damage to the blood vessels through greater oxidative stress, which in turn causes increases in blood pressure, type 2 diabetes, strokes, heart attacks and heart failure.

Particulate Matter

The worst health effects of airborne pollution come from the inhalation of particulate matter (PM) – often referred to as aerosols. PM refers to the solid particles and liquid droplets that float for a time in the air.

Some are visible with the naked eye, but most can only be seen through a microscope. Some of these microscopic particles are naturally occurring. They include fragments of mineral dust, sea salt, or volcanic ash. Most are man-made particles (or droplets) composed of black carbon, soot, sulphates, nitrates, ammonia, or flecks of heavy metals, such as cadmium, lead and mercury.

The two forms of PM which have been implicated in brain research are PM2.5 (less than 2.5 microns in diameter – that’s about 28 times smaller than a human hair) and ultrafine PM (UFPM) (particles less than 100 nanometers in diameter – that’s 40 times smaller again).

These microscopic particles pose the greatest risks to health, as they are capable of penetrating deep into the lungs and from there into the bloodstream and the major organs.

Particulates are released during the combustion of fossil fuels and biomass. Common sources include: all engines (diesel/petrol); solid-fuel combustion of coal, lignite, heavy oil for energy production; industrial furnaces involved in cement manufacture, smelting and similar activities; the burning of wood, charcoal, crop residues/stubble, or other biomass material. For more details on the health effects of PM pollutants, see below.

Black Carbon

Black carbon is a common component of PM2.5. It is one of the main short-lived climate pollutants (SLCPs), yet one of the largest contributors to global warming after CO2. Inhalation of black carbon is linked to a number of health conditions such as asthma, respiratory and cardiovascular disease, cancer, and birth defects.

Nitrogen Dioxide (NO2)

Nitrogen dioxide, mainly discharged by power plants, factories and vehicle engines, is another important component of particulate matter and ozone. Exposure to NO2 aggravates symptoms of bronchitis and asthma, and can lead to respiratory infections and lung problems. Some evidence indicates that NO2 may be responsible for cardiovascular as well as respiratory diseases.

Ground-level Ozone (O3)

Ground-level ozone is one of the main constituents of urban photochemical smog. Exposure to O3 can cause asthma, breathing problems, reduced lung function and several respiratory conditions. Ozone also acts as a greenhouse gas, trapping heat in the troposphere. For more about the health effects of ozone, see below.

A major contributor to ground-level ozone in cities is the internal combustion engine, which spews out a range of toxic gases from its tailpipe. This is why electric vehicles (cars, buses and trucks) are so much better for our respiratory health, because they emit no gases of any description.

Sulfur Dioxide (SO2)

SO2 is mostly produced from the burning of coal and petroleum as well as the smelting of mineral ores that contain sulfur. Exposure to fine sulfate particles – for which SO2 is the precursor – interferes with the respiratory system and the lungs, and also causes irritation of the eyes. It can also exacerbate asthma and chronic bronchitis, and heighten the risk of infections. SO2 also combines with water in the atmosphere to create acid rain.

Although sulfur dioxide levels have fallen in many cities in Western Europe and the United States, they remain higher in a number of cities in Eastern Europe, South America and Asia, where coal-fired power plants and domestic heating systems are still prevalent.

Deaths from Ambient Air Pollution

Estimates of fatalities from outdoor pollution vary. According to WHO, outdoor air pollutants caused 4.2 million deaths in 2016. These fatalities accounted for:

  • 26 percent of all respiratory infection deaths.
  • 25 percent of all chronic obstructive pulmonary disease (COPD) deaths.
  • 17 percent of all coronary heart disease and stroke.
  • 16 percent of all lung cancer deaths. 3

However, two new studies disagree with WHO’s older estimates of outdoor air pollution (see below).

Deaths from Household Pollution

According to WHO, indoor air pollution in 2016 was responsible for 3.8 million deaths. 4 These fatalities accounted for:

  • 50 percent of pneumonia deaths in children under 5 years of age.
  • 28 percent of pneumonia deaths in adults.
  • 25 percent of all deaths due to COPD in developing countries.
  • 17 percent of all deaths due to lung cancer.
  • 12 percent of all deaths due to strokes.
  • 11 percent of all deaths due to coronary heart disease. 5

These figures do not include deaths and serious injuries from burns, which are a regular hazard for household occupants who depend upon open fires for cooking and heat. Young children, in particular, are especially at risk.

Deaths from All Air Pollution

World Health Organization (WHO)

According to WHO, a combination of ambient and household airborne pollution is responsible for 8 million deaths annually. Roughly 4.2 million from outdoor pollutants; 3.8 million from indoor pollutants.

Of these deaths:

  • 34 percent are due to coronary heart disease.
  • 21 percent are due to pneumonia.
  • 20 percent are due to strokes.
  • 19 percent are due to COPD.
  • 7 percent are due to lung cancer.

Health Effects Institute (HEI)

According to the “State of Global Air (2019)” a key report compiled by the Health Effects Institute (HEI), total air pollution (from particulate matter, ozone, and household air pollution) caused almost 5 million deaths globally — nearly 1 in every 10 deaths — in 2017.

The report found that the 10 countries that suffered the highest mortality from airborne pollutants were: India (1.2 million), China (1.2 million), Pakistan (128,000), Indonesia (124,000), Bangladesh (123,000), Nigeria (114,000), the United States (108,000), Russia (99,000), Brazil (66,000), and the Philippines (64,000).

New Health Studies into Ambient Air Pollution Doubles WHO’s Estimates

A new 2020 international study into outdoor air quality, conducted by leading scientists and published in the journal Cardiovascular Research, disagrees with WHO’s estimate of 4.2 million annual deaths. Using the new Global Exposure Mortality Model (GEMM), the study finds that outdoor pollution accounts for 8.8 million deaths annually – more than twice the WHO figure. For example, the revised number of fatalities for China is 2.8 million deaths each year, two-and-a-half times the WHO estimate. 6

The conclusions of the new study are remarkably similar to another recent study (2018) which reported 8.9 million premature deaths from airborne pollutants. 7

Other findings from the 2020 study include:

• Coronary heart disease and stroke account for almost half of the 8.8 million deaths, with respiratory diseases, type 2 diabetes and high blood pressure accounting for most of the rest. Only 6 percent of mortality from polluted air is due to lung cancer.

• Two-thirds of deaths are caused by human-made pollution, mostly due to fossil fuel use. In high-income countries the figure rises to 80 percent.

• In China, air pollution reduces the average lifespan by 4.1 years. In India, the reduction is 3.9 years, and in Pakistan 3.8 years.

• Regional blackspots include India’s Uttar Pradesh (population 200 million) where PM2.5 pollution alone cuts life expectancy by 8.5 years. In China’s Hebei Province (population 74 million) the reduction is nearly six years. In Africa, the average loss of lifespan is 3.1 years, although in Chad, Sierra Leone, Central African Republic, Nigeria and Cote d’Ivoire – it rises to between 4.5 and 7.3 years. Among developed nations, the worst pollution is found in Eastern Europe: in Bulgaria, Hungary and Romania.

• Airborne pollution accounts for 19 times more deaths each year than malaria, nine times more than HIV/AIDS, and three times more than alcohol.

Whose Health is Most at Risk from Air Pollution?

Overall, those whose health is most at risk from airborne pollutants are people who live in ‘developing countries’. This is because they use high-emission coal-fired power plants to generate electricity, high-emission furnace and factory technologies to make steel, cement and other industrial products, and because anti-pollution legislation is either non-existent or barely enforced. Traditional practices such as the burning of crop stubble and other biomass residues are another contributing factor. See for example: Asian Brown Cloud: Toxic Haze.

Poverty is even more important when it comes to indoor pollution. Most global deaths from household pollutants are caused by inefficient cooking practices involving wood burning on open fires, or in crude stoves powered by solid fuels and/or kerosene. These involve the poorest inhabitants of the developing world.

By comparison, high-income countries experience much lower levels of power plant and factory emissions, but persistent levels of urban smog caused by vehicle emissions. In the home, the number of pollution-related deaths is very small, due to larger living space, more windows, more modern cooking facilities and the wider use of relatively ‘clean’ energy such as electricity and newer central heating systems.

But even in affluent countries there is no room for complacency. America is a case in point.

Los Angeles Air Pollution
Air pollution over the city of Los Angeles. Thousands of oil wells and refineries cover the Los Angeles Basin and account for nearly 40 percent of California’s economic output. Recent research by the Advancing Earth and Space Science (AGU) shows however that the region’s six largest refineries are individually emitting 300–700 percent more pollution than is being reported. Photo: David Iliff/CC BY-SA 3.0

Air Pollution in the United States

After decades of progress, air quality in the United States seems to have taken a dip over the last few years. 8 That’s according to data provided in mid-2019 by the U.S. Environmental Protection Agency (EPA) concerning the health effects of airborne pollution.

The EPA recorded 15 percent more days with unhealthy air in the country in 2018 and 2017 compared to the preceding three years 2013-2016. On average, in 2017 and 2018 there were nearly 140 occasions when a city’s air quality exceeded the worst two categories — “very unhealthy” and “hazardous” — with the air quality index showing more than 200. That’s more than two-and-a-half times the average AQI of 55 achieved during the period 2013-2016.

Meantime, the American Lung Association’s 2019 “State of the Air” report found that 141.1 million people lived in counties with unhealthy concentrations of either PM2.5 or ground-level ozone, an increase of more than 7.2 million Americans since the previous report in 2018. Further more, 8 cities reported their highest number of days with unhealthy particle pollution since the U.S. started monitoring this particular pollutant 20 years ago. 9

EPA-Approved Air Quality Causes 200,000 U.S. Deaths

A decade-long cohort U.S. study into the health effects of air pollution, that monitored the progress of more than 4.5 million – mostly male, mostly white – U.S. veterans, was recently published in the Journal of the American Medical Association. The study found that almost 200,000 deaths were attributable to poor air quality. The big shocker was that virtually all (99 percent) of the victims were exposed to levels of air pollution that the Environmental Protection Agency (EPA) says is safe! 10

The study linked nine causes of death with levels of PM2.5 in the air from victims’ individual zip codes. The causes of death were: cardiovascular disease (55,000 deaths), stroke (40,000 deaths), chronic kidney disease, COPD, type 2 diabetes, high blood pressure, lung cancer (17,500 deaths), pneumonia and dementia (19,000 deaths).

How Many Americans Die From Air Pollution Each Year?

How many people die each year from air pollutants in the United States? The answer is, no one knows for sure. This is no reflection on the dangers of PM2.5 or ozone (the biggest killers). It’s a reflection of how difficult it is to trace a clear link between the pollution inhaled and cause of death. The above-mentioned JAMA study succeeded in establishing clear links in the cases it reviewed, but few nationwide studies – using up-to-date data – have appeared.

According to a 2013 MIT study into the health effects of air pollution in the U.S., particulate matter (PM2.5) was estimated to account for about 200,000 premature deaths, while ground level ozone accounted for about 10,000 deaths. 11

According to a 2019 study, PM2.5 pollution is estimated to account for 107,000 premature deaths in 2011, at a cost to society of $886 billion. According to the study, emissions of PM2.5 are densest in urban areas, notably along the East Coast. However, agricultural emissions – of ammonia and nitrates from fertilizers and manure – account for about 15 percent of the deaths. 12

Health Effects of Ozone/Smog

The health effects of air pollution in cities are well-documented. Ground level ozone and photochemical smog typically materialize in and around urban areas during warm dry periods. Photochemical smog involves the emission of vehicle exhaust fumes (composed of PM2.5, carbon monoxide, nitrogen oxides, sulfur dioxide and VOCs) which react to create ozone (O3) in sunlight. It can also include ammonia, dust and smoke from surrounding fields.

In the short-term, this type of chemical pollution irritates the eyes, nose, throat and lungs of children and old people, as well as those who work outside. Those who suffer from asthma or allergies are most vulnerable, since smog tends to trigger asthmatic or allergy attacks. Long-term exposure to ozone/smog is associated with serious respiratory diseases, COPD, lung cancer and heart disease.

Health Effects of Particulate Matter & Aerosols

Pollution from PM2.5 and aerosols is associated with several serious non-communicable diseases (NCDs), including cerebrovascular disease, heart disease, kidney disease, COPD, type 2 diabetes, hypertension, lung cancer, pneumonia, certain birth defects, Alzheimer’s disease and dementia.

According to the 2019 World Air Quality Report 13 compiled by Swiss company IQAir, the health effects of air pollution – notably PM10 and PM2.5 – are worst in Asia, where most manufacturing takes place.

• In China, 98 percent of cities fail to meet WHO air quality guidelines, and 53 percent of cities fail to meet China’s own lower targets. That said, over the past decade, China’s capital Beijing has more than halved its annual PM2.5 levels, and in 2019 dropped out of the ‘top 200 most polluted cities’ altogether.

• In India, cities on average, emit 5 times more PM2.5 than the amount permitted by the World Health Organization.

• Cities in India and Pakistan again dominate the category of the ‘world’s most polluted cities for PM2.5’ in 2019. Of the 30 most polluted cities, 21 are located in India, while 5 are in Pakistan.

• Southeast Asia suffers particularly from the health effects of air pollution. The region is experiencing rapid industrialization. As a result, Vietnam’s Hanoi and Indonesia’s Jakarta have overtaken Beijing, for the first time, in the list of the world’s most PM2.5 polluted capital cities.

• Among OECD countries, South Korea was the most polluted country for PM2.5 during 2019.

Indoor pollution. Woman using firewood to cook a meal for her family in Ghana.
Woman using firewood to cook a meal for her family in Ghana. Photo: © K. Trautmann/CCAFS,CC BY-NC-SA 2.0

Naturally Occurring PM2.5 Pollution

Up to one third of airborne particulates and aerosols are naturally occurring, although they are just as deadly.

According to the 2019 World Air Quality Report, wildfires had a major impact on the air quality of cities and countries around the world, including: Russia, Singapore, Thailand, Malaysia, Indonesia, Australia, Brazil, and Los Angeles. In North Africa, and western China, desertification and sandstorms are the main natural contributors to unhealthy air.

Volcanic pollutants in the form of aerosols and PM2.5 are a small but regular feature of the atmosphere. However, it is usually difficult to separate the separate health effects of gas, ash, and aerosols of the various chemicals outgassed. 14

Health Impact of Greenhouse Gases

The health effects of air pollution are mostly the result of fossil fuel combustion. As we have seen, 66 percent of airborne pollution-related deaths are due to the burning of fossil fuels. In high-income countries the number rises to 80 percent.

As we know, whenever fossil fuels like coal or petroleum or natural gas are burned, they release emissions of greenhouse gases that ramp up the greenhouse effect in the atmosphere, which in turn leads to rising temperatures around the globe.

These rising temperatures are responsible for drying out forests in Alaska, Siberia, Canada, California and Oregon, as well as bushland across southeast Australia. Which is why all these regions have experienced massive wildfires over the past few years. These fires produce huge emissions of carbon dioxide, which ramp up the greenhouse effect once again, and the whole cycle is repeated. And, as we have seen, these fires also produce vast quantities of PM2.5, some of which ends up in our lungs and bloodstream.

Other effects of global warming on humans are well documented and include: exposure to extreme weather events (e.g. storms, flooding, extreme heat, drought) more diseases (e.g. malaria) and loss of food (due to weather-related crop failure or yield reduction). And health effects of air pollution.


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  4. “Household Pollution.” WHO. []
  5. “Household air pollution and health.” WHO. []
  6. “Loss of life expectancy from air pollution compared to other risk factors: a worldwide perspective.” Jos Lelieveld, Andrea Pozzer, Ulrich Poschl, Mohammed Fnais, Andy Haines, Thomas Munzel. Cardiovascular Research (2020) 116, 1910–1917. []
  7. “Global estimates of mortality associated with long-term exposure to outdoor fine particulate matter.” Burnett R, et al. Proc Natl Acad Sci USA 2018; 115:9592–9597. []
  8. “US air quality is slipping after years of improvement.” Seth Borenstein, Nicky Forster. June 18, 2019. []
  9. “More than 4 in 10 Americans Live with Unhealthy Air; Eight Cities Suffered Most Polluted Air Ever Recorded.” American Lung Association. []
  10. “Burden of Cause-Specific Mortality Associated with PM2.5 Air Pollution in the United States.” Benjamin Bowe, et al. JAMA Netw Open. 2019;2(11) []
  11. “Air pollution and early deaths in the United States. Part I: Quantifying the impact of major sectors in 2005.” Fabio Caiazzo et al. Atmospheric Environment Volume 79, November 2013, Pages 198-208. []
  12. “Fine-scale damage estimates of particulate matter air pollution reveal opportunities for location-specific mitigation of emissions.” Andrew L. Goodkind, Christopher W. Tessum, Jay S. Coggins, Jason D. Hill, Julian D. Marshall. PNAS (2019) 116 (18) 8775-8780; April, 2019. []
  13. “2019 World Air Quality Report.” []
  14. “Particulate Matter (PM) and Aerosol” The International Volcanic Health Hazard Network (IVHHN) []
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