With new national clean air protections in place, a UNC-Chapel Hill study suggests that future air quality measures may need to be more localized.
The study, led by professor Sarav Arunachalam with UNC’s Institute for the Environment, looked at the national trends of tiny air-polluting particles known as fine particulate matter, or PM2.5.
“These are really small particles, but then they tend to form quite a bit of adverse air pollution health impacts,” Arunachalam said. Those health impacts range from respiratory to cardiovascular issues. “This is one of the largest health risks we have in the world. About 7 million people die prematurely, annually, on a global basis based upon exposure to fine particulate matter.”
Arunachalam’s study, which was published on ScienceDirect, found that the national average concentration of PM2.5 has decreased since 2006. In 2020, the national average was 8.20 micrograms per cubic meter, down from 2006’s average of 11.38.
The Environmental Protection Agency recently lowered the allowable levels of PM2.5 from 12 to 9 micrograms per cubic meter. But, Arunachalam said that new limit doesn't address how the chemical composition of PM2.5 can vary based on location.
“The regulations are currently based upon total mass without focusing on what the components are,” Arunachalam said.
For example, North Carolina's PM2.5 composition is affected by its abundance of trees, which Arunachalam said produce about 90% of the state’s volatile organic compounds. Those compounds can form toxic aerosols associated with PM2.5. Conversely, the chemical makeup of PM2.5 in the Western U.S. may be more influenced by soot-producing wildfires.
Two locations could, therefore, both meet the EPA’s limit for PM2.5 levels, but the chemical makeup of the particles in one location could be more toxic than the other. That could then have greater health impacts.
With that in mind, Arunachalam said that targeting those regional differences in pollution may be key to future air quality improvement efforts that benefit public health.
While PM2.5 composition can change based on location, the study also found composition has changed over time.
“The inorganic components have come down,” Arunachalam said. Those are made up of sulfate, nitrate and ammonium. He attributed their reduction to increased regulations on things like coal-burning power plants. “But,” Arunachalam added, “the organics have not come down. That's what we need to focus on going forward.”
Namely, carbon has become a “bigger piece of the pie,” according to Arunachalam. He said that the transportation sector is one area where addressing carbon emissions could have powerful co-benefits. Automobile exhaust can emit black carbon, or soot. If reduced, Arunachalam said that would have both climate and health benefits.
Given how PM2.5 trends have changed across time and space, Arunachalam said he wants to see more monitoring at state and federal levels to best address local causes of air pollution.
“We cannot control what we don't measure,” Arunachalam said. “We need to first understand where the high levels are and use that to start to look at component-specific health impacts more and more. I think that's where we'll get the most gains in public health.”