Years of scientific research have clearly established that particle pollution and ozone are a threat to human health at every stage of life, increasing the risk of premature birth, causing or worsening lung and heart disease, and shortening lives. Some groups of people are more at risk of illness and death than others, because they are more likely to be exposed, or are more vulnerable to health harm, or often both.

Air pollution can harm children and adults in many ways


  • Wheezing and coughing,
  • Shortness of breath,
  • Asthma attacks,
  • Worsening COPD,
  • Lung cancer


  • Premature death,
  • Susceptibility to infections,
  • Heart attacks and strokes,
  • Impaired cognitive functioning,
  • Metabolic disorders,
  • Preterm births and low birth weight

Health Effects of Particle Pollution

Particle pollution – also known as particulate matter – is a deadly and growing threat to public health in communities around the country. The more researchers learn about the health effects of particle pollution, the more dangerous it is recognized to be.

Particle pollution refers to a mixture of tiny bits of solids and liquids in the air we breathe. Particle pollution comes from many sources. Factories, power plants, and diesel- and gasoline-powered vehicles and equipment either directly emit fine particles or generate other pollutants, such as nitrogen oxides (NOx) and sulfur oxides (SOx), known as precursors because they can then form into fine particles in the atmosphere. Other sources of particle pollution include wildfires, burning wood in wood stoves or residential fireplaces and burning biomass for electricity.

Researchers and regulators categorize particles according to size, grouping them as coarse, fine and ultrafine. Coarse particles, called PM10, can include wind-blown dust, ash, pollen and smoke. Fine particles, PM2.5, are most often a by-product of burning wood or fossil fuels, and may include components such as toxic compounds, salts and metals. The tiniest are called ultrafine particles, or PM0.1. They are also produced by combustion, and are included in the larger category of PM2.5.

Individual fine particles are too small to be visible, but when pollution levels are high, they can make the air appear thick and hazy.

Sources of particle pollution include motor vehicles, factories, power plants, equipment, wood burning and wildfires.

The differences in size make a big difference in how particles affect our health. Our bodies’ natural defenses help us to keep the coarse particles we inhale out of the deepest parts of our lungs, although these particles do deposit in the larger airways. However, those defenses do not keep smaller fine or ultrafine particles from penetrating deep into the lungs and even all the way into the air sacs. Many of these particles get trapped there, while the smallest are so tiny that they can pass from the air sacs into the bloodstream and disperse to other organs of the body.

Particle pollution can be very dangerous to breathe, especially at higher concentrations. It can trigger illness, hospitalization and premature death. Researchers estimate that PM2.5 is responsible for nearly 48,000 premature deaths in the United States every year.1

Short-Term Exposure

Short-term spikes in particle pollution that last from a few hours to a few days can kill. Premature deaths from breathing these particles can occur on the very day that particle levels are high, or up to a month or two afterward. Most premature deaths are from respiratory and cardiovascular causes. Particle pollution does not just make people die a few days earlier than they might otherwise—in many cases these deaths would not have occurred for years if the air were cleaner.2

Studies linking short-term exposure to PM2.5 to death from all causes have been accumulating for a number of years. Taken together, this body of research provides consistent evidence of positive associations between particle pollution and mortality across diverse geographic locations and in populations with a wide range of demographic characteristics. In 2019, an international study looking at 499 cities across the globe reinforced these consistent findings.3

Exposure to even low levels of fine particles can be deadly. Looking nationwide in a 2017 study, researchers found that older adults faced a higher risk of premature death even when levels of short-term particle pollution remained well below the current national standard. This was consistent whether the older adults lived in cities, suburbs or rural areas.4 Another study published in 2018 analyzed mortality data from 135 U.S. cities and found a causal relationship with exposure to PM2.5 at concentrations below the federal standard.5

Particle pollution also has many other harmful effects, ranging from decreased lung function to heart attacks. Extensive research has linked short-term increases in particle pollution to:

  • increased mortality in infants;6
  • increased hospital admissions for cardiovascular disease, including heart attacks and strokes;7
  • increased hospital admissions and emergency department visits for chronic obstructive pulmonary disease (COPD);8
  • increased severity of asthma attacks and hospitalization for asthma among children.9,10

Year-Round Exposure

Decades of research have firmly established that breathing particle pollution day in and day out can also be deadly. Across numerous seminal studies that looked at different groups of people living in different parts of the country, the results consistently showed a clear relationship between long-term exposure to particulate matter and mortality.11

Research using publicly available data on a cohort of more than one million adults in the U.S. reconfirmed that long-term exposure to PM2.5 was associated with elevated risks of early death. The increased risk was primarily associated with death from cardiovascular and respiratory causes, including heart disease, stroke, influenza and pneumonia. Researchers also found a similar association between exposure to fine particle pollution and an increased risk of death from lung cancer among never-smokers.12 Another study of 68.5 million Medicare-enrolled adults in the United States between 2000 and 2016 found a 6-8% increase in risk of all-cause mortality for every 10µg/m3 increase in the annual average PM2.5.13

Research has also linked year-round exposure to particle pollution to a wide array of serious health effects at every stage of life, from conception through old age. Among individuals who are pregnant, fetuses and children, long-term particle pollution exposure is linked to: 

  • Increased risk of preterm birth and low birth weight;14 
  • Increased fetal and infant mortality;15
  • Impaired neurological development and cognition;16
  • Reduced lung development and impaired lung function in children;17
  • Higher likelihood of children developing asthma.18

In adults, long-term particle pollution exposure is linked to:

  • Increased risk from existing cardiovascular and respiratory disease, including a worsening of heart disease, atherosclerosis and COPD;19,20
  • Higher likelihood of developing diabetes and subsequent complications; 21,22
  • Higher likelihood of getting lung cancer and of dying from it;23
  • Impaired cognitive functioning and an increased risk of Parkinson’s disease, Alzheimer’s disease and other dementias later in life.24,25 
  • Increased risk of clinical depression and anxiety.26

The good news is that cleaning up particle pollution makes a difference. Research has shown a consistent relationship between decreasing PM2.5 concentrations and improving respiratory health in children and reduced mortality of adults in communities that have reduced their levels of year-round particle pollution.27,28

Anyone who lives where particle pollution levels are high is at risk. Some people face greater risk, however, based on their underlying health and other characteristics. [See the People at Risk section for more information about vulnerable groups] Research has shown that the groups at the greatest risk from particle pollution include:

  • Individuals who are pregnant and fetuses;29
  • Infants, children and older people (> 65 years of age);30
  • People with lung disease, especially asthma, but also people with COPD;31
  • People with cardiovascular disease;32
  • People with lung cancer;33
  • People of color;34
  • Current or former smokers;35
  • People with low incomes;36 and
  • People who are obese or have diabetes.37

Health Effects of Ozone Pollution

Ground-level ozone, sometimes known as smog, is one of the most widespread and dangerous pollutants in the United States. Scientists have studied the effects of ozone on human health for decades. Hundreds of studies have confirmed that ozone harms people at levels currently found in many parts of the United States. 

Ozone is a gas composed of molecules with three oxygen atoms. (The oxygen we need for life is made up of molecules with two oxygen atoms.) Ozone forms in the lower atmosphere when a combination of pollutants, usually nitrogen oxides (NOx) and volatile organic compounds (VOCs), “cook” together in sunlight through a series of chemical reactions. NOand VOCs are produced primarily when fossil fuels such as gasoline, diesel, oil, natural gas or coal are burned or when solvents and some other chemicals evaporate. NOx is emitted from power plants, motor vehicles and other sources of high-heat combustion. VOCs are emitted from motor vehicles, oil and gas operations, chemical plants, refineries, factories, gas stations, paint, consumer products and other sources. 

If these ingredients are present under the right conditions, they react to form ozone. Sunlight is key, with higher temperatures increasing ozone production. Because the reactions take place in the atmosphere, ozone often shows up downwind of the sources of the original emissions, sometimes many miles from where it formed.

Ozone air pollution is sometimes called ground-level ozone, to distinguish it from the much higher-altitude stratospheric ozone layer that protects people from damaging ultraviolet rays from the sun.

Ozone gas is a powerful lung irritant. When it is inhaled into the lungs, it reacts with the delicate lining of the small airways, causing inflammation and other damage that can impact multiple body systems. Ozone exposure can also shorten lives.

Ozone has a serious effect on the respiratory system, both in the short term and over the course of years of exposure. 

When ozone levels are high, many people experience breathing problems such as chest tightness, coughing and shortness of breath, often within hours of exposure. Even healthy young adults may experience respiratory symptoms and decreased lung function.38

Other breathing problems that have been tied to short-term exposure to ozone include:

  • Worsening of symptoms, increased medication use and increased emergency department visits and hospital admissions for people with asthma and COPD;39
  • Susceptibility to respiratory infections such as pneumonia, resulting in an increased likelihood of emergency department visits and hospitalizations.40

Living with ozone pollution long-term may cause lasting damage to respiratory health, including:

  • Development of new cases of asthma in children;41
  • Damage to the airways, leading to development of COPD;42
  •  Increased allergic response.43

The inflammation and systemic stress caused by short- and long-term exposure to ozone can also do damage to tissues, genes and proteins throughout the body, which can cause or worsen other disease conditions over time. These include:

  • Increased risk of metabolic disorders, including glucose intolerance, hyperglycemia and diabetes;44
  • Impact on the central nervous system, including brain inflammation, structural changes and possible increased risk of cognitive decline;45, 46
  • Increased likelihood of reproductive and developmental harm, including reduced fertility, preterm birth, stillbirth and low birth weight;47, 48
  • Possible cardiovascular effects – although according to the most recent EPA review, the evidence linking ozone to heart disease, heart failure and stroke is mixed.49

The damage ozone does to the body can be deadly. Recent research has affirmed earlier findings that short-term exposure to ozone, even at levels below the current standard, likely increases the risk of premature death, particularly for older adults.50 There is also a growing body of evidence that long-term exposures to ambient ozone may be associated with an increased risk of cardiovascular and respiratory disease mortality.51

Anyone who spends time outdoors where ozone pollution levels are high may be at risk. Some people face a higher-than-average risk, however, because of their underlying health and other characteristics. [See the People at Risk section for more information about vulnerable groups.] Research has shown that the groups at greatest risk from ozone pollution include:

  • Pregnant people and fetuses;52
  • Children;
  • Anyone 65 and older;
  • People with existing lung disease such as asthma and COPD;
  • People who work or exercise outdoors.53

Air Pollution and COVID-19

Both ozone and particle pollution can impact the functioning of the immune system and increase susceptibility to respiratory infections. Air pollution also increases the risk of chronic lung and cardiovascular diseases that put people at higher risk of poor outcomes from COVID-19.   It should come as no surprise, then, that a growing body of research has found an association between exposure to even low levels of air pollution and an increased risk of severe illness and death from COVID-19. People living with chronic conditions, the elderly, people of color and those living in low-wealth communities are more vulnerable to poor outcomes.54,55 A 2022 study in California found that people living in the most polluted areas of the state had a 20% higher risk of COVID infection and a 51% higher risk of death than residents in the least polluted areas.56

People at Risk

The health burden of air pollution is not evenly shared. Some people are more at risk of illness and death from air pollution than others. Several key factors affect an individual’s level of risk:

  • Exposure – Where someone lives, where they go to school and where they work makes a big difference in how much air pollution they breathe. In general, the higher the exposure, the greater the risk of harm.
  • Susceptibility – Individuals who are pregnant and their fetuses, children, older adults and people living with chronic conditions, especially heart and lung disease, may be physically more susceptible to the health impacts of air pollution than other adults.
  • Access to healthcare – Whether or not a person has health coverage, a healthcare provider, and access to linguistically and culturally appropriate health information may influence their overall health status and how they are impacted by environmental stressors like air pollution.
  • Psychosocial stress – There is increasing evidence that non-physical stressors such as poverty, racial/ethnic discrimination and migration status can amplify the harmful effects of air pollution.

These risk factors are not mutually exclusive and often interact in ways that lead to significant health inequities among subgroups of the population. Taken all together, these high-risk categories account for a large proportion of the U.S. population.

Research has shown that people of color are more likely to be exposed to air pollution and more likely to suffer harm to their health from air pollution than white people.57,58 Much of this inequity can be traced to the long history of systemic racism in the United States. Practices such as redlining, the discriminatory outlining of so-called “riskier” neighborhoods by mortgage lenders, institutionalized residential segregation in the 20th century, impairing the ability of many people of color to build wealth and limiting their mobility and political power. Over the years, decision-makers have found it easier to place sources of pollution, such as power plants, industrial facilities, landfills and highways, in economically disadvantaged communities of color than in more affluent, predominantly white neighborhoods. The resulting disproportionate exposure to air pollution has contributed to high rates of emergency department visits for asthma and other diseases.59,60

People of color are also more likely than white people to be living with one or more chronic conditions that make them more susceptible to the health impact of air pollution, including asthma and diabetes.61

There is evidence that having low income or living in lower income areas puts people at increased risk from air pollution, although the correlation is not as strong as with race and ethnicity.62,63 People living in poverty are more likely to live in close proximity to sources of pollution and have fewer resources to relocate than people with more financial security.64 Poverty itself, along with the problems that beset many low-income communities, such as lack of safety, green space, and high-quality food access, have been associated with increased psychosocial distress and chronic stress, which in turn make people more vulnerable to pollution-related health effects.65 People with low income also have lower rates of health coverage and less access to quality and affordable health care to provide relief to them when they get sick.

Children are both more susceptible to harm from air pollution and more likely to be exposed than adults. The growth and development of a child’s lungs and breathing ability start in utero and continue into early adulthood. Long-term exposure to particle pollution during pregnancy and early childhood has been linked to reduced lung growth and long-term exposure to ozone has been linked to increased potential for the development of asthma. The developing brain and heart may also be affected, with life-long consequences.66 In addition, the body’s defenses that help adults fight off infections are still developing in children. Children have more respiratory infections than adults, which also seems to increase their susceptibility to air pollution.67

Children breathe more rapidly and inhale more air relative to their size than do adults. They are more likely to spend time outdoors, running around, being active and breathing hard. Consequently, they are more exposed to polluted outdoor air than adults typically are.

Much of the illness and premature death caused by air pollution occurs in older adults, who are at increased risk of harm for several reasons. As a person ages, the normal process of thinning and weakening of the lung tissue and the supporting muscle and bones of the ribcage results in diminishing lung function over time. The impairment that results from exposure to air pollutants then has an add-on effect, putting stress on the lungs and heart. Older people are also more likely to be living with chronic diseases, and there is evidence that co-existing chronic lung, heart or circulatory conditions may worsen following exposure to environmental pollutants. 68

The strength of the immune system also declines with age, leaving older people at greater risk of contracting infections and less able to get them under control before they become serious. Because exposure to air pollution increases susceptibility to respiratory infections, it also increases the risk of severe illness and death in older adults. 

For the millions of people in the U.S. living with illnesses such as asthma, COPD, diabetes, heart disease and lung cancer, exposure to air pollution places them at greater risk of harm to their health than those without disease. The cellular injury and systemic inflammation triggered by breathing ozone and particle pollution put additional stress on people’s lungs, heart and other organs already compromised by disease. This can result in a worsening of symptoms, increased medication use, more frequent emergency department visits and hospitalizations, an overall reduced quality of life and far too often premature death.

Pregnancy is always a susceptible time for both the individual who is pregnant and the developing fetus. The pregnant body undergoes dramatic physiological changes in hormone levels, metabolism and circulation throughout months of gestation. The rapid and complex development of the fetus is a precisely timed and sequenced process. The inflammation and oxidative stress resulting from exposure to air pollution during pregnancy can increase the risk of hypertensive disorders, including preeclampsia, and lead to intrauterine inflammation and damage to the placenta that can disrupt the growth and development of the fetus. Fetal health may also be impacted in a number of ways by environmental contaminants that have been shown to cross the placenta. 69

Exposure to both ozone and particle pollution during pregnancy is associated with premature birth, low birth weight and stillbirth. These risks are amplified when the individual who is pregnant is also at higher risk of health harm from air pollution in other ways, such living in poverty or having asthma. 70

There is some recent evidence suggesting that current and former smokers are at greater risk of health harm from exposure to fine particle pollution compared with never-smokers. They are more likely to develop lung cancer and to die prematurely.71 Smoking damages the lungs, heart, blood vessels and other organs.72 This impairment leaves the person with a smoking history more vulnerable to the health impact of air pollution than a never-smoker.

Did You Know?

  1. Nearly four in ten people in the U.S. live where the air they breathe earned an F in “State of the Air” 2024.
  2. More than 131 million people live in counties that received an F for either ozone or particle pollution in “State of the Air” 2024.
  3. Nearly 44 million people live in counties that got an F for all three air pollution measures in “State of the Air” 2024.
  4. Breathing ozone irritates the lungs, resulting in inflammation—as if your lungs had a bad sunburn.
  5. Breathing in particle pollution can increase the risk of lung cancer.
  6. Particle pollution can cause early death and heart attacks, strokes and emergency room visits.
  7. Particles in air pollution can be smaller than 1/30th the diameter of a human hair. When you inhale them, they are small enough to get past the body's natural defenses.
  8. Ozone and particle pollution are both linked to increased risk of premature birth and lower birth weight in newborns.
  9. If you live or work near a busy highway, traffic pollution may put you at greater risk of health harm.
  10. People who work or exercise outside face increased risk from the effects of air pollution.
  11. Millions of people are especially vulnerable to the effects of air pollution, including children, older adults and people with lung diseases such as asthma and COPD.
  12. People of color and people with lower incomes are disproportionately affected by air pollution that puts them at higher risk for illness.
  13. Air pollution is a serious health threat. It can trigger asthma attacks, harm lung development in children, and even be deadly.
  14. You can protect yourself by checking the air quality forecast in your community and avoiding exercising or working outdoors when unhealthy air is expected.
  15. Climate change enhances conditions for ozone pollution to form and makes it harder clean up communities where ozone levels are high.
  16. Climate change increases the risk of wildfires whose smoke spreads dangerous particle pollution.
  17. Policymakers at every level of government must take steps to clean the air their constituents breathe.
  18. The nation has the Clean Air Act to thank for decades of improvements in air quality. This landmark law has successfully driven pollution reduction for over 50 years.
  19. Particle pollution exposure from wildfire smoke harms health in ways that range from mild irritation to serious illness and premature death.
  20. Recent updates to the Air Quality Index give the public more accurate information about the health risk from air pollution, and when to take measures to protect themselves on bad air days.
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  1. Health Effects Institute. State of Global Air. Boston, MA. 2020.

  2. U.S. EPA. Integrated Science Assessment for Particulate Matter. December 2019 EPA/600/R-19/188. Section 11.1.

  3. Liu C, Chen R, Sera RF, Vicedo‑Cabrera AM, Guo Y, Tong S, Coelho MSZS, Saldiva PHN, Lavigne E, Matus P, Valdes Ortega PN, Osorio Garcia S, Pascal M, Stafoggia M, Scortichini M, Hashizume M, Honda Y, Hurtado‑Diaz M, Cruz J, Nunes B, Teixeira JP, Kim H, Tobias A, Íñiguez C, Forsberg B, Åström C, Ragettli MS, Guo Y-L, Chen B-Y, Bell ML, Wright CY, Scovronick N, Garland RM, Milojevic A, Kyselý J, Urban A, Orru H, Indermitte E, Jaakkola JJK, Ryti NRI, Katsouyanni K, Analitis A, Zanobetti A, Schwartz J, Chen J, Wu T, Cohen A, Gasparrini A, Kan H. Ambient Particulate Air Pollution and Daily Mortality in 652 Cities. N Engl J Med. 2019; 381(8):705-15.

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  27. U.S. EPA. 2019, Section 5.2.11.

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  29. Bekkar B et al. 2020.

  30. U.S. EPA. 2019, Section

  31. U.S. EPA. 2019, Section 12.3.5.

  32. U.S. EPA. 2019, Section 12.3.1.

  33. U.S. EPA. 2019, Section

  34. U.S. EPA. 2019, Section 12.5.4.

  35. U.S. EPA. 2019, Section 12.6.1.

  36. U.S. EPA. 2019, Section 12.5.3.

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  40. U.S. EPA. 2020, Section 3.1.7.

  41. U.S. EPA. 2020, Section

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