New tougher U.S. air pollution standards shaped by Harvard Chan School research

Pollution pours from factory smokestacks at sunset

February 14, 2024 – Stricter new federal regulations on deadly fine particulate air pollution in the U.S. were announced on February 7—and Harvard T.H. Chan School of Public Health research played a key role in the decision.

Many studies published in recent years by Harvard Chan researchers have provided strong evidence showing the link between fine particulate pollution, disease, and premature death. These studies provided important evidence in the EPA’s decision to strengthen the new regulations, according to Marc Weisskopf, Cecil K. and Philip Drinker Professor of Environmental Epidemiology and Physiology. Weisskopf served from 2021 to 2022 on a panel advising the EPA on fine particulate matter.

Francesca Dominici, Clarence James Gamble Professor of Biostatistics, Population, and Data Science, who has co-authored numerous studies on the health impacts of PM2.5, called the new regulations “extremely important, and a huge victory in public health.” She added, “The School should be really proud because this is a huge public health victory, and we don’t get these very often.”

Fine particulate pollution (PM2.5) is made up of tiny particles that are 30 times smaller than the width of a human hair. These particles can penetrate deep into the lungs. In addition to being linked to early death, PM2.5 exposure has also been shown to lead to worsened asthma, heart attacks, stroke, and other diseases. Major sources of PM2.5 include the burning of fossil fuels, agriculture, and industry. Wildfire smoke and dust also contribute to the problem.

Under the new regulations, annual exposure to fine particulate pollution must be limited to 9 μg/m(micrograms per cubic meter of air), down from the current limit of 12. According to the EPA, the new limit, when fully implemented, could prevent up to 4,500 premature deaths and 290,000 lost workdays per year.

Douglas Dockery, John L. Loeb and Frances Lehman Loeb Professor of Environmental Epidemiology, Emeritus, credited a number of Harvard Chan School Department of Environmental Health experts, including Dominici, Joel Schwartz, professor of environmental epidemiology, and Antonella Zanobetti, principal research scientist, for their pivotal air pollution research. He noted that they’ve been able to look at air pollution’s impact across the U.S. by using large Medicare datasets assembled by Dominici and added that Schwartz provided the data on being able to estimate air pollution levels for individual people across the U.S., taking into account both location and time. “That has really revolutionized our knowledge about the health effects of air pollution and has provided great context for setting the new standards,” said Dockery.

Dockery himself played a key role in influencing national air quality standards, as lead author of the groundbreaking Six Cities study, published three decades ago. In that study, researchers followed more than 8,000 adults from six U.S. cities that had different air pollution levels, finding that there was a 26% difference in survival between residents of the least-polluted cities and the most-polluted. The study also found that PM2.5 was the most dangerous kind of air pollution.

“We’ve seen big improvements in air quality since then,” Dockery noted. “Industry has always complained that curbing air pollution was going to be too expensive and would hurt the economy—and it is continuing to say that now—but we’ve achieved progress even as the population has gone up, GDP has increased dramatically, and the number of cars on the road has spiked. It’s a testament to our ability to clean up the air. It’s pretty extraordinary to think about it.”

Recent Harvard Chan School studies that have shed light on the dangers of PM2.5 and that factored into the new standards include a July 2020 study that showed that strengthening U.S. limits on PM2.5 concentrations could save thousands of lives. Harvard Chan co-authors included then-doctoral student and lead author Xiao Wu, as well as Dominici, Schwartz, and Danielle Braun, principal research scientist. An October 2021 study, led by postdoctoral fellow Mahdieh Danesh Yazdi, found that even small increases in long-term exposure to both particle and gaseous air pollutants increased the risk of premature death, even within existing standards. Dominici, Schwartz, and nine other Harvard Chan researchers were co-authors.

A low-enough limit?

Schwartz called the new standards “good but not great.” That’s because he and other experts, along with some public health groups such as the American Lung Association, had hoped that the EPA would lower the PM2.5 limit even further, to 8 μg/m3. “I sent very detailed comments to the EPA on this proposal, pointing out that many studies had shown that PM2.5 impacts on serious illness and hospitalizations come from concentrations even below 9,” he said. “They chose to ignore that.”

Schwartz added that, taking into account how long it’s likely to take for the new standards to truly take effect—six or seven years—they don’t have nearly as much teeth as they could have. Already, average PM2.5 concentrations across the U.S. are just over 9 μg/m3, he said, explaining that after the EPA sets new pollution standards, it can take a couple of years for the agency to assess which counties across the U.S. aren’t meeting them. States then have two years to develop an implementation plan. And once a state implementation plan is approved, industry has another two years to install new pollution controls. In the meantime, said Schwartz, air pollution in the U.S. is likely to decrease further because of ongoing changes including the decommissioning of coal plants, new solar and wind energy options, and increasing use of electric vehicles—meaning that most counties across the U.S. are likely to be under the 9 μg/m3 limit anyway. “If the EPA had set the limit at 8 μg/m3, it would cost more, but there would be a lot more [health] benefits,” he said.

Dominici agreed. “We had an important paper in the New England Journal of Medicine that showed that a limit of 8 μg/m3 would have been better—especially for Black Americans—but the fact that the limit is being lowered to 9 μg/m3 is still important. We will all be breathing cleaner air.”

Dockery also acknowledged that a lower PM2.5 limit could have gone further to prevent health harms. “As researchers and scientists, we’re trying to provide the best information possible on the science,” he said. “But ultimately this is a political decision that has to be made. It is always a compromise.”

Looking ahead

Dominici noted that she and colleagues plan to increasingly focus their research on vulnerable communities—communities of color and those with low socioeconomic status—which are more likely to be located near heavier pollution sources such as highways and industrial sites, and where it may be more difficult to reduce pollution levels.

Dominici also has questions about how the nation will address PM2.5 pollution produced by wildfires. She noted that many counties in California, for example, are not in compliance with air quality standards because of the many wildfires that occur there, but that it’s not clear if the EPA will approach that non-compliance differently than non-compliance from industry.

“I think that the scientific community really needs to focus on these two issues—vulnerable communities and pollution from wildfires—now more than ever,” she said.

Karen Feldscher

Photo: iStock/eric1513