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  5. Particle Pollution

Particle Pollution

Ever look at dirty tailpipe exhaust?

The dirty, smoky part of that stream of exhaust is made of particle pollution. Overwhelming evidence shows that particle pollution—like that coming from that exhaust smoke—can kill. Particle pollution can increase the risk of heart disease, lung cancer and asthma attacks and can interfere with the growth and work of the lungs.

What Is Particle Pollution?

Particle pollution refers to a mix of tiny solid and liquid particles that are in the air we breathe. Many of the particles are so small as to be invisible, but when levels are high, the air becomes opaque. Nothing about particle pollution is simple. In fact, it is so dangerous that it can shorten your life.

Size matters. Particles themselves are different sizes. Some are one-tenth the diameter of a strand of hair. Many are even tinier; some are so small they can only be seen with an electron microscope. Because of their size, you cannot see the individual particles. You can only see the haze that forms when millions of particles blur the spread of sunlight.

Researchers categorize particles according to size, grouping them as coarse, fine and ultrafine. Coarse particles (shown as blue dots in the illustration) fall between 2.5 microns and 10 microns in diameter and are called PM 10-2.5. Fine particles (shown as pink dots in the illustration) are 2.5 microns in diameter or smaller and are called PM2.5. Ultrafine particles (not shown) are smaller than 0.1 micron in diameter1 and are small enough to pass through the lung tissue into the blood stream, circulating like the oxygen molecules themselves. No matter what the size, particles can harm your health.

The differences in size make a big difference in where particles affect us. Our natural defenses help us to cough or sneeze some coarse particles out of our bodies. However, those defenses do not keep out smaller fine or ultrafine particles. These particles get trapped in the lungs, while the smallest are so minute that they can pass through the lungs into the bloodstream, just like the essential oxygen molecules we need to survive.

“A mixture of mixtures.” Because particles form in so many ways, they can be composed of many different compounds. Although we often think of particles as solids, not all are. Some are liquid; some are solids suspended in liquids. As EPA put it, particles are really “a mixture of mixtures.”2

The mixtures differ between different regions in the United States and in different times of the year. Much of that comes from the sources that produce the particles. For example, nitrate particles from motor vehicle exhaust form a larger proportion of the unhealthful mix in the winter in western states, especially California and portions of the Midwest. By contrast, eastern states have more sulfate particles than the West on average, largely due to the high levels of sulfur dioxide emitted by large, coal-fired power plants.3

Who Is at Risk?

Anyone who lives where particle pollution levels are high is at risk. Some people face higher risk, however. People at the greatest risk from particle pollution exposure include:

  • Infants, children and teens;1
  • People with lung disease, especially asthma, but also people with chronic obstructive pulmonary disease (COPD);2
  • People with cardiovascular disease;3
  • People of color;4
  • Current or former smokers;5
  • People with low incomes;6 and
  • People who are obese.7

People with lung cancer also appear to be at higher risk from particle pollution, according to a 2016 study of more than 350,000 patients in California. Researchers looked at the exposure they experienced between 1988 and 2011 and found that where higher concentrations of particle pollution existed, people with lung cancer had poorer survival.8

EPA had concluded in the past that people with diabetes are also at higher risk of harm from particle pollution. In their most recent review of people at risk, they revised that decision. The evidence of increased risk remains strong, especially given the increased risk of cardiovascular disease from diabetes. Research has found evidence that long-term exposure to particle pollution may increase the risk of developing diabetes. Two independent reviews of published research found that particle pollution may increase the risk of developing type 2 diabetes mellitus.9

What Can Particles Do to Your Health?

Particle pollution can be very dangerous to breathe depending on the level. Breathing particle pollution may trigger illness, hospitalization and premature death, risks that are showing up in new studies that validate earlier research.

Thanks to steps taken to reduce particle pollution, good news is growing from researchers who study the drop in year-round levels of particle pollution.

  • Looking at air quality in 545 counties in the U.S. between 2000 and 2007, researchers found that people had approximately four months added to their life expectancy on average due to cleaner air. Women and people who lived in urban and densely populated counties benefited the most.1
  • Another long-term study of people in six U.S. cities tracked from 1974 to 2009 added more evidence of the benefits. The findings suggest that cleaning up particle pollution had almost immediate health benefits. The researchers estimated that the U.S. could prevent approximately 34,000 premature deaths a year if the nation could lower annual levels of particle pollution by 1 µg/m3.2

These studies add to the growing research that cleaning up air pollution improves life and health.

Short-Term Exposure Can Be Deadly

First, short-term exposure to particle pollution can kill.1 Peaks or spikes in particle pollution can last from hours to days. Premature deaths from breathing these particles can occur on the very day that particle levels are high, or within one to two months afterward. Particle pollution does not just make people die a few days earlier than they might otherwise—these deaths would not have occurred so early if the air were cleaner.

Even low levels of particles can be deadly. A 2016 study found that people aged 65 and older in New England faced a higher risk of premature death from particle pollution, even in places that met current standards for short-term particle pollution.2 Another study in 2017 looked more closely at Boston and found a similar higher risk of premature death from particle pollution in a city that meets current limits on short-term particle pollution.3 Looking nationwide in a 2017 study, researchers found more evidence that older adults faced a higher risk of premature death even when levels of short-term particle pollution remained well below the current national standards. This was consistent whether the older adults lived in cities, suburbs or rural areas.4 Some of the strongest research has documented that short-term exposure to particle pollution causes premature death from respiratory and cardiovascular causes.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 ischemic heart disease;7
  • increased hospital admissions and emergency department visits for COPD;8
  • increased hospitalization for asthma among children;9and
  • increased severity of asthma attacks in children.10

A 2008 study of lifeguards in Galveston, TX, provided evidence of the impact of short-term exposure to particle pollution on healthy, active adults. Testing the breathing capacity of these outdoor workers several times a day, researchers found that many lifeguards had reduced lung volume when fine particle levels were high. Because of this research, Galveston became the first city in the nation to install an air quality warning flag system on the beach.11

Year-Round Exposure

Breathing high levels of particle pollution day in and day out can also be deadly, as landmark studies in the 1990s conclusively showedi and as later studies verified.2 Recent research has confirmed that long-term exposure to particle pollution still kills, even with the declining levels in the U.S. since 2000 3 and even in areas, such as New England, that currently meet the official limit, or standard, for year-round particle pollution.4

In 2013, the International Agency for Research on Cancer (known as IARC), part of the World Health Organization, concluded that particle pollution causes lung cancer. The IARC based its decision on the review of multiple studies from the U.S., Europe, and Asia and the presence of carcinogens on the particles.5

Research has also linked year-round exposure to particle pollution to:

  • development of asthma in children;6
  • worsening of COPD in adults;7
  • slowed lung function growth in children and teenagers;8
  • increased risk of death from cardiovascular disease;9 and
  • increased risk of heart attacks and strokes.10

Studies examining the impact on the nervous system of long-term exposure to particle pollution have found links to cognitive affects in adults including reduced brain volume, cognitive decrements and dementia.11 Scientists have found evidence that particle pollution may impact pregnancy and birth outcomes, such as preterm birth, low birth weight and fetal and infant mortality.12

The EPA is conducting their new review of the current research on particle pollution. Their findings from the last review, completed in December 2019,13 are highlighted in the box below

EPA Concludes Fine Particle Pollution Poses Serious Health Threats (2019)

    • Causes early death (both short-term and long-term exposure)
    • Causes cardiovascular harm (e.g., heart attacks, strokes, heart disease, congestive heart failure)
    • Likely to cause respiratory harm (e.g., worsened asthma, worsened COPD, inflammation)
    • Likely to cause cancer
    • Likely to cause harm to the nervous system (e.g. reduced brain volume, cognitive effects) 
    • May cause reproductive and developmental harm

—U.S. Environmental Protection Agency, Integrated Science Assessment for Particulate Matter, December 2019. EPA 600/R-19/188

Where Does Particle Pollution Come From?

Particle pollution forms through two separate processes—mechanical and chemical.

Mechanical processes break down bigger bits into smaller bits with the material remaining essentially the same, only becoming smaller. Dust storms, construction and demolition, mining operations, and agriculture are among the activities that produce particles. Tire, brake pad and road wear can also create particles.

Combustion of carbon-based fuels generates most of the fine particles in our atmosphere. Burning wood in residential fireplaces and wood stoves as well as wildfires, agricultural fires and prescribed fires are some of the largest sources. Wildfires are growing, particularly in the Mountain West because of climate change. These processes create about 36 percent of fine particles.1 Burning fossil fuels in factories, power plants, diesel- and gasoline-powered motor vehicles (cars and trucks) and equipment emits a large part of the raw materials for fine particles.

Chemical processes in the atmosphere create most of the tiniest fine and ultrafine particles in the air. Burning fuels, other human activity and natural sources emit gases that form particles in the air. These gases can oxidize and then condense to become a particle of a simple chemical compound. Or they can react with other gases or particles in the atmosphere to form a particle of a different or of multiple chemical compounds. Particles formed by this latter process come from the reaction of elemental carbon (soot), heavy metals, sulfur dioxide (SO2), nitrogen oxides (NOx), ammonia (NH3) and volatile organic compounds with water and other compounds in the atmosphere.2

Are Some Particles More Dangerous than Others?

With so many sources of particles, researchers want to know if some particles pose greater risk than others. Researchers are exploring possible differences in health effects of the sizes of particles and particles from different sources, such as diesel particles from trucks and buses or sulfates from coal-fired power plants. Recent studies have tried to answer this question. So far, the answers are complicated.

Each particle may have many different components. The building blocks of each can include several biological and chemical components. Bacteria, pollen and other biological ingredients can combine in the particle with chemical agents, such as heavy metals, elemental carbon, dust and secondary species like sulfates and nitrates. These combinations mean that particles can have complex effects on the body.1

Some studies have found that different kinds of particles may have greater risk for different health outcomes. 2,3,4

Other studies have identified the challenges of exploring all the kinds of particles and their health effects with the limited monitoring across the nation.5,6Some particles serve as carriers for other chemicals that are also toxic, and the combination may worsen the impact.7,8

The best evidence shows that having less of all types of particles in the air leads to better health and longer lives.

  1. U.S. EPA. Integrated Science Assessment for Particulate Matter (Final Report). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-08/139F, 2009. Available at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=216546.

  2. U.S. EPA. Air Quality Criteria for Particulate Matter, October 2004.

  3. U.S. EPA. Integrated Science Assessment for Particulate Matter, December 2019. EPA/600/R-19/188.

  4. U.S. EPA, 2019. Section 12.5.1.1.

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

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

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

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

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

  10. U.S. EPA 2019, Section 12.3.3.

  11. Eckel SP, Cockburn M, Shu YH, Deng H, Lurmann FW, Liu L Gilliland FD. Air pollution affects lung cancer survival. Thorax, 2016: 71:891-898.

  12. Rao X, Patel P, Puett R and Rajogpalan S. Air pollution as a risk factor for type 2 diabetes. Toxicological Sciences. 2015; 143 (2): 231-241; Eze IC, Hemkens LG, Bucher HC, Hoffman B, et al. Association between ambient air pollution and diabetes mellitus in Europe and North America: Systematic review and meta-analysis. Environ Health Perspect. 2015; 123 (5): 381-389.

  13. Correia AW, Pope CA III, Dockery DW, Wang Y, Ezzati M, Domenici F. Effect of air pollution control on life expectancy in the United States: An analysis of 545 U.S. Counties for the period from 2000 to 2007. Epidemiology. 2013; 24(1): 23-31.

  14. Lepeule J, Laden F, Dockery D, Schwartz J. Chronic exposure to fine particles and mortality: An extended follow-up of the Harvard Six Cities Study from 1974 to 2009. Environ Health Perspect. 2012; 120: 965-970. U.S. EPA, 2019, Section 6.1.9.

  15. U.S. EPA, 2019, Section 6.1.9.

  16. Shi L, Zanobetti A, Kloog I, Coull BA, Koutrakis P, Melly SJ, Schwartz JD. Low-concentration PM2.5 and mortality: estimating acute and chronic effects in a population-based study. Environ Health Perspect. 2016; 124:46-52. http://dx.doi.org/10.1289/ehp.1409111.

  17. Schwartz J, Bind MA, Koutrakis P. Estimating causal effects of local air pollution on daily deaths: Effect of low levels. Environ Health Perspect. 2017; 125:23-29. http://dx.doi.org/10.1289/EHP232.

  18. Di Q, Dai L, Wang Y, Zanobetti A, Choirat C, Schwartz JD, Dominici F. Association of Short-Term Exposure to Air Pollution with Mortality in Older Adults. JAMA. 2017; 318: 2446-2456.

  19. U.S.EPA, 2019, Section 11.1

  20. U.S. EPA, 2019, Section 9.1.2.6

  21. U.S. EPA, 2019. Section 6.1.2.

  22. U.S. EPA, 2019, Section 5.1.2.1.1.

  23. U.S. EPA, 2019. Section 5.1.2.1.

  24. U.S. EPA, 2019. Section 5.1.2.2.1.

  25. Thaller EI, Petronell SA, Hochman D, Howard S, Chhikara RS, Brooks EG. Moderate increases in ambient PM2.5 and ozone are associated with lung function decreases in beach lifeguards. J Occp Environ Med. 2008; 50: 202-211.

  26. Dockery DW et al. An association between air pollution and mortality in six U.S. cities. N Engl J Med. 1993; 329: 1753-1759. Pope CA et al. Particulate air pollution as a predictor of mortality in a prospective study of U.S. adults. Am J Respir Crit Care Med. 1995; 151: 669-674.

  27. U.S. EPA, 2019. Section 11.2.2.1.

  28. Thurston GD, Ahn J, Cromar KR, Shao Y, Reynolds H, et al. Ambient particulate matter air pollution exposure and mortality in the NIH-AARP Diet and Health Cohort. Environ Health Perspect. 2015. 124: 484–490; Lepeule J, Laden F, Douglas Dockery D, and Schwartz J. Chronic exposure to fine particles and mortality: An extended follow-up of the Harvard Six Cities Study from 1974 to 2009. Environ Health Perspect. 2012; 120: 965–970.

  29. Shi L, Zanobetti A, et al. Low-concentration PM2.5 and mortality: estimating acute and chronic effects in a population-based study. Environ Health Perspect. 2015; 124: 46-52.

  30. Hamra GB, Guha N, Cohen A, Laden F, Raaschou-Nielsen O, Samet JM, Vineis P, Forastiere F, Saldiva P, Yorifuji T, and Loomis D. Outdoor particulate matter exposure and lung cancer: A systematic review and meta-analysis. Environ Health Perspect. 2014: 122: 906-911.

  31. U.S. EPA, 2019. Section 5.2.3.1.

  32. U.S. EPA, 209. Section 5.2.5.

  33. U.S. EPA, 2019. Section 5.2.2.2.1.

  34. U.S. EPA, 2019. Section 6.2.10

  35. U.S. EPA, 2019. Section 6.2.2 and Section 6.2.3.

  36. U.S. EPA, 2019. Section 8.2.9

  37. U.S. EPA, 2019. Section 9.1.2, especially Section 9.1.2.3.1. and Section 9.1.2.6.

  38. U.S. EPA, 2019.

  39. U.S. EPA, 2019, Section 2.3.1.1.

  40. U.S. EPA, 2019.Section 2.3.2.

  41. Morakinyo OM, Mokgobu MI, Mukhola MS, Hunter RP. Review: Health outcomes of exposure to biological and chemical components of inhalable and respirable particulate matter. Int. J. Environ. Res. Public Health. 2016: 592.

  42. Thurston GD, et al. Ischemic heart disease mortality and long-term exposure to source-related components of U.S. fine particle air pollution. Environ Health Perspect; 2016; 124:785–794. http://dx.doi.org/10.1289/ehp.1509777.

  43. Bell ML, et al. Associations of PM2.5 constituents and sources with hospital admissions: analysis of four counties in Connecticut and Massachusetts (USA) for persons ≥ 65 years of age. Environ Health Perspect. 2014: 122: 138–144; http://dx.doi.org/10.1289/ehp.1306656.

  44. Ebisu K, Bell ML. Airborne PM2.5 chemical components and low birth weight in the Northeastern and Mid-Atlantic regions of the United States. Environ Health Perspect. 2012; 120: 1746–1752; http://dx.doi.org/10.1289/ehp.1104763.

  45. Levy JI, Diez D, Dou Y, Barr CD, Dominici F. A meta-analysis and multisite time-series analysis of the differential toxicity of major fine particulate matter constituents. Am J Epidemiology. 2012; 175(11): 1091-1099. doi:10.1093/aje/kwr457.

  46. Dai L, Zanobetti A, Koutrakis P, Schwartz JD. Associations of fine particulate matter species with mortality in the United States: A multicity time-series analysis. Environ Health Perspect. 2014; 122(8): 837- 842. doi:10.1289/ehp.1307568.Pope CA III, Burnett RT, Thurston GD, Thun MJ, Calle EE, Krewski D, Godleski JJ. Cardiovascular mortality and year-round exposure to particulate air pollution: Epidemiological evidence of general pathophysiological pathways of disease. Circulation. 2004; 109: 71-77.

  47. Morakinyo et al., 2016

  48. Cassee FR, Héroux M-E, Gerlofs-Nijland ME, Kelly FJ. Particulate matter beyond mass: recent health evidence on the role of fractions, chemical constituents and sources of emission. Inhalation Toxicology. 2013; 25(14): 802-812. doi:10.3109/08958378.2013.850127.

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