Particle Pollution

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 PM_2.5. Ultrafine particles (not shown) are smaller than 0.1 micron in diameter 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.”

The mixtures differ between different regions in the United States and at different times of the year based on the sources that produce the particles. For example, nitrate particles from motor vehicle exhaust form a larger proportion of the unhealthy particle mix in the winter in western states, especially California and portions of the Midwest. In 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.

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:

• Pregnant individuals;
• Infants, children and teens;
• Older adults (>65 years of age);
• People with lung disease, such as asthma and chronic obstructive pulmonary disease (COPD);
• People with cardiovascular disease;
• People who are obese or have diabetes;
• Current or former smokers;
• People with low socioeconomic status; and
• People of color.

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.

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.
• 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.

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. 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. 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. 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. Some of the strongest research has documented that short-term exposure to particle pollution causes premature death from respiratory and cardiovascular causes.

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;
• increased hospital admissions for cardiovascular disease, including heart attacks and ischemic heart disease;
• increased hospital admissions and emergency department visits for COPD;
• increased hospitalization for asthma among children; and
• increased severity of asthma attacks in children.

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.

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. Recent research has confirmed that long-term exposure to particle pollution still kills, even with the declining levels in the U.S. since 2000 and even in areas, such as New England, that currently meet the official limit, or standard, for year-round particle pollution.

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.

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

• higher likelihood of children developing asthma;
• worsening of COPD in adults;
• slowed lung function growth in children and teenagers;
• increased risk of death from cardiovascular disease; and
• increased risk of heart attacks and strokes;
• higher likelihood of getting lung cancer; and 
• higher likelihood of developing diabetes

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. 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.

The official national limits on fine particle pollution, also called the National Ambient Air Quality Standard, were last strengthened by EPA in 2012. However, newer research shows that both short-term and long-term exposure to particle pollution can cause serious harm even at much lower levels. In fact, there is no safe threshold to breathe in fine particles.