The EPA announced in January that it is considering changing its air quality guidelines to align with the latest science suggesting adverse health effects for people exposed to PM2.5—airborne particles smaller than 2.5 micrometers.
The agency is considering changing the National Ambient Air Quality Standard (NAAQS) for annual PM2.5 from 12 to 9–10 micrograms per cubic meter (µg/m3) averaged over 3 years.
But the agency also said it would take public comments on lowering the standard to as little as 8 µg/m3 or as high as 11 µg/m3. The agency opted to keep the 24-hour PM2.5 concentration standard of 35 µg/m3.
Lowering the EPA guidelines would force utilities, manufacturers, and farmers to upgrade factories, practices, and equipment to release less pollution.
Some industry groups called the proposed changes unnecessary, whereas environmental and justice groups criticized the EPA for not going far enough.
Twice the number of people die from causes related to air pollution in the United States each year than from car crashes. Tighter guidelines would particularly benefit Black, Hispanic, and low-income communities, which face the brunt of air pollution.
Human Health Risk
PM2.5 consists of airborne particles 30 times smaller than the diameter of a human hair. When inhaled, the particles travel deep into the lungs, infiltrating the alveoli and traveling into the blood. PM2.5 is thought to accumulate in the lungs over time, causing inflammation.
The pollutant has been linked to myriad health issues, including asthma, preterm birth, heart disease, respiratory infections, and premature death. In the United States, PM2.5 causes nearly 11,000 excess deaths each year, nearly 3,000 incidences of lung cancer, and 18,000 morbidities, according to data from New York University’s Marron Institute of Urban Management dashboard.
Burning gasoline, oil, diesel fuel, or wood releases PM2.5 particles. Electric utilities and industrial boilers are responsible for about half of the direct PM2.5 pollution in the United States. Another 40% comes from industrial equipment such as metal smelters, petroleum refineries, and cement kilns. Tilling and harvesting farms and applying fertilizer and manure create additional pollution from agriculture. Cars and trucks also release fine-particle pollution.
Once aloft, these particles can stay in the air for long periods and travel far distances.
Passed in 1970, the Clean Air Act requires the EPA to set standards for particulate matter and five other pollutants. The EPA must periodically review the standards to ensure adequate health and environmental protection.
The agency has updated either the annual or short-term PM2.5 standard about every decade since the 1990s. But in December 2020, the Trump administration opted to keep standards the same.
The Biden administration said it is now reconsidering the limits because the latest science suggests that the current standards don’t adequately protect public health.
Roughly 8,800 more people could be saved from asthma onset with an 8 versus 10 µg/m3 limit, according to the EPA’s Regulatory Impact Analysis published in late 2022. In the same analysis, the EPA estimated that 7,500 deaths would be avoided in 2032 if levels were below 8 µg/m3 versus 10 µg/m3.
In the EPA’s Integrated Science Assessment, published in 2019, the agency reviewed the most recent animal toxicology studies, controlled human exposure studies, and epidemiologic studies and found that the evidence supported and strengthened the health findings from past research.
Science Shows Environmental Injustices
The agency found “strong evidence” that Black and Hispanic populations, on average, experience higher PM2.5 exposures and related health risks than non-Hispanic white populations. It also found that people in lower socioeconomic positions are exposed to higher concentrations.
Annual PM2.5 concentration was 14% higher for Black people in the United States than for white people in 2016, according to a Nature study published in 2022.
The EPA’s Regulatory Impact Analysis predicted that lowering the annual PM2.5 standards will lessen pollution exposure for marginalized groups, particularly if limits are lowered to 8 µg/m3. Hispanic people would experience 4.8% less PM2.5 pollution at 8 µg/m3; at 10 µg/m3, the change drops to 1.5%. Asian people would see similar relief.
A New England Journal of Medicine study found that if the standard were lowered to 8 µg/m3, there would be a 6% decrease in exposure for low-income Black and low-income white adults.
Environmental and Health Organizations Debate Limit
Wide-sweeping policies such as the PM2.5 rule affect human health, governmental regulation, and industrial activities. While the EPA deliberates, opinions about the best level of PM2.5 are swirling.
The Clean Air Scientific Advisory Committee, an independent panel of experts that provides advice to the EPA regarding the NAAQS, recommended that the annual average should be between 8 and 10 µg/m3.
The American Lung Association said the EPA’s proposal to limit pollution to 9–10 µg/m3 “misses the mark” and called for an 8 µg/m3 annual limit and a 24-hour limit of 25 µg/m3. The World Health Organization (WHO) recommended that standards be set at an annual limit of 5 µg/m3 and a 24-hour limit of 15 µg/m3. Implementing the WHO’s standard worldwide would avoid almost 80% of deaths from PM2.5, according to research by the WHO.
Environmental groups criticized that the proposed standards don’t go far enough. Earthjustice, a progressive environmental nonprofit, said the proposed regulation fails to make the sweeping improvements that the latest science calls for.
“With PM2.5, the EPA knows that kills people,” said Seth Johnson, a senior attorney at Earthjustice. “And for PM2.5, the evidence of disparate impact is really strong. We know it affects people of color—particularly Black people—at least in part due to differences in exposure.”
Industry Weighs In
Currently, 12 cities have annual PM2.5 levels above today’s EPA standard. If the limit is lowered to 9 µg/m3, at least 32 cities will exceed the standard.
Though industry groups have concerns about financing the implementation of new standards, the EPA must consider only what protects human health and welfare in its decision.
Lowering the limit will be a harmful burden for the industry, according to a statement from the National Association of Manufacturers (NAM), a trade association for manufacturing companies.
“Let manufacturers do what they do best: innovate and deploy modern technologies to protect the environment, while creating jobs and strengthening the economy,” said NAM president and CEO Jay Timmons in a press release.
The Fertilizer Institute, an advocacy organization for the fertilizer industry, stated that the new standards would threaten the production of fertilizer domestically. Nisei Farmers League in California said in a statement that many farmers are still working to comply with the current standard and that doing so requires new equipment and production systems.
Lowering the standard to 11 µg/m3 would be challenging for industries, especially in places where monitored concentrations are already high, but “it wouldn’t cause large-scale impacts across the country,” wrote Leslie Fifita and Robynn Andracsek at Providence Engineering, an engineering and environmental consulting firm in Louisiana and Texas, in an email. “However, a reduction down to 8 µg/m3 would create complex compliance issues with respect to PM2.5 attainment areas, air permitting, and air dispersion modeling.”
With scientific findings suggesting larger public health benefits for lower PM2.5 levels, as well as concerns from industry groups about reaching the standards, time will tell which value of PM2.5 the EPA settles on. The agency hosted a public 60-day comment period and hearings this spring, and the final decision may come later this year or next.
—Jenessa Duncombe (@jrdscience), Staff Writer