What is particulate matter? 

Air pollution is a combination of solid and gas particles in the air. The most common and harmful air pollutants include particulate matter, nitrogen dioxide, ozone and sulfur dioxide. 

Particulate matter is a mix of solids and liquids suspended in the air. These suspended particles are known to cause health problems and may include chemicals, dust, pollen, car emissions and more. While many air pollutants are harmful, the degree to which they affect the human body is linked to the size of the particulate matter.

Scientists classify particles by their size and group them into categories: course, fine and ultrafine. Coarse particles are between 2.5 and 10 microns in diameter and are termed PM 10 to 2.5. Fine particles are 2.5 microns and smaller and are termed PM 2.5. Ultrafine particles are smaller than 0.1 microns in diameter and can enter the bloodstream, circulating through the body. 

Though most air pollution is considered harmful, smaller particles are considered more dangerous to the body. Larger particles can be seen with the naked eye and are considered less dangerous because they can be caught in the nasal canal, sneezed or coughed out. Smaller particles however, can have adverse effects on human health; fine particles, like PM 2.5, can pass through lung tissue and can cross into the bloodstream. 

How are particles formed? 

Larger particles are produced mechanically by breaking up large solids. These newly formed coarse particles can then travel by air from construction sites, agricultural processes, uncovered soil, roads, and more. 

The amount of energy that it takes to break particles increases as the size of the particles get smaller. So, it takes more energy to break a smaller particle than it does a large one. This creates a lower bound for the size of the coarse particles, which are about 1µm in diameter. 

Smaller particles are mainly formed from gases. They are formed as a result of chemical reactions that occur in the atmosphere, burning fuels, forest fires and more. These particles can also be directly emitted from power plants and other industry-related processes. 

Why is it dangerous? 

Coarse particles are usually not of high concern, as they usually only irritate the eyes, nose and throat. However, numerous scientific studies have linked fine and ultrafine particulate matter to a variety of serious health problems including premature deaths in people with heart or lung disease, heart attacks, irregular heartbeats, asthma, cardiovascular disease, decreased lung function, airway irritation, coughing and difficulty breathing. 

“All people are likely susceptible to the adverse effects of air pollution. But people who have chronic lung diseases such as asthma are more susceptible,” said Dr. Nadia Hansel, who studies lung issues at Johns Hopkins University.

A 2013 WHO assessment concluded that outdoor air pollution is carcinogenic to humans, with a clear association between PM 2.5 and increased cancer incidence. 

Disparities in particulate pollution

Overall, studies have shown that the highest burden of air pollutants fall to minority and lower socioeconomic communities.  

In 2016, outdoor air pollution in cities and rural areas was estimated to cause 4.2 million premature deaths worldwide per year due to exposure to PM 2.5. Individuals living in lower socioeconomic communities and countries disproportionately experienced the burden of outdoor air pollution with 91% of deaths occurring in low- and middle-income countries. 

Additionally, a large study found that Hispanics, Asians, and Black people in the United States  consistently had a higher risk for premature deaths from particle pollution compared to white Americans. The study also found that income did not drive the differences in these communities, suggesting that the impact of other factors like chronic stress as a result of discrimination might be influencing the results. 

Income also plays a role in air pollution. Pollution sources, like factories and chemical plants,  tend to be located in areas near disadvantaged communities. Low-income households are more likely to live in areas with more air pollution due to lower rent prices and affordability. 

In Atlanta, Georgia, a study found that particle pollution increased the risk of asthma attacks in zip codes where the level of poverty was high. Additionally, low-income individuals tend to have restricted access to routine medical care, which can exacerbate health conditions further and worsen the impact of environmental pollutants.

“When people with poorly controlled asthma are exposed to low levels of ozone, the amount of inflammation in the lungs goes way up,” said Dr. Daryl Zeldin, a lung and environmental health science expert at NIH. “As a result, air passages narrow, which makes it much harder to breathe.”

In combination with limited or inaccessible health care, increased exposure to particulate matter disproportionately harms minority and disadvantaged communities.

“Poor communities, frequently communities of color, but not exclusively, suffer disproportionately,” said Carol Browner, who headed the Environmental Protection Agency during the Clinton administration. “If you look at where our industrialized facilities tend to be located, they’re not in the upper middle class neighborhoods.”

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