Stronger air pollution standards in U.S. would have significant public health benefits

image of smoke stacks reflecting in a person's glasses

May 26, 2021 –Reducing certain air pollutants in the U.S. by small amounts would prevent thousands of early deaths each year among elders, according to new research led by Harvard T.H. Chan School of Public Health.

The study, which focused on fine particulate matter (PM2.5), nitrogen dioxide (NO2), and ozone (O3), also found that even when levels of these pollutants met or fell below the Environmental Protection Agency’s (EPA) current National Ambient Air Quality Standards, they were still associated with significant mortality in elders. The authors said the findings raise serious concerns that the country’s current air quality standards do not sufficiently protect public health.

“Clearly the current national air pollution standards are entirely outdated and the progress in reducing air pollution is stalled,” said Joel Schwartz, professor of environmental epidemiology and senior author of the study. “The findings of this study signal a very clear message to policy makers: More rigorous PM2.5 and NO2 standards and a long-term O3 standard are absolutely necessary to protect public health, especially the health of elders.”

The study was published in Environmental Health on May 6, 2021.

To analyze the issue, the team used national Medicare data collected between 2000 and 2016 and predicted ZIP code–level estimates of ambient air pollution levels based on ground monitoring data, satellite data, meteorological conditions and several other factors. They focused specifically on establishing what is known as the “causal dose-response” relationship between the air pollutants and mortality among the Medicare population. A dose-response relationship can show how exposures to a certain amount of a substance—in this case, individual air pollutants—changes physiological function and health condition. The model created for this study also enabled the researchers to predict what would happen at the population level if exposures to these air pollutants changed.

In addition to determining that PM2.5, O3, and NO2 are all linked with significant harmful effects on human health, even at low levels, the researchers also found that substantial health gains can be achieved through small reductions in exposures. For instance, the study showed that lowering PM2.5 concentration by less than 1 microgram per cubic meter and lowering concentrations of O3 by less than 2 parts per billion and NO2 by approximately 3 parts per billion would prevent 65,935 early deaths per year among elders.

Moreover, according to Schwartz, the study highlighted the urgent need for the EPA to better regulate levels of O3, a gas that occurs naturally in the stratosphere but can also form at the ground level as a result of pollution from diesel engines and other sources undergoing chemical reactions in the presence of sunlight. At the ground level, O3 is associated with numerous health risks, especially for children, the elderly, and people who have asthma and similar conditions. There is currently no long-term exposure standard for O3, just a daily one.

“For O3, the EPA has focused on bringing down the number of peak days in the summer while producing little change in the long-term average exposure between spring and fall,” Schwartz said. “Our study shows that this is a mistake, and people are dying from it.”

Corresponding author Yaguang Wei, a doctoral candidate in the Department of Environmental Health, said that causal modeling can help provide precises predictions of how changes to air quality standards will affect public health. “We think this study can be used to help EPA, the World Health Organization, and others set their air quality standards and estimate the health benefits of specific policies, such as replacing diesel vehicles with cleaner alternatives,” Wei said.

Other Harvard Chan School co-authors of the paper include Mahdieh Danesh Yazdi, Francesca Dominici, and Antonella Zanobetti.

Chris Sweeney

Photo composite: Kent Dayton