Wildfires have offset 20 years of air quality gains in US West: study

The frequency and ferocity of wildfires across the U.S. West have negated the improvements in air quality achieved over the past two decades, a new study has found.

From 2000 through 2020, air pollution has deteriorated in this part of the country due to these blazes, causing a surge of 670 premature deaths annually during that period, according to the study, published on Monday in The Lancet Planetary Health.

Wildfires, the researchers determined, have managed to “undercut successful federal efforts” from the Environmental Protection Agency (EPA), which has worked to improve air quality primarily through reduction in vehicular emissions.

“Our air is supposed to be cleaner and cleaner due mostly to EPA regulations on emissions, but the fires have limited or erased these air-quality gains,” co-first author Jun Wang, chair of the University of Iowa’s Department of Chemical and Biochemical Engineering, said in a statement.

“In other words, all the efforts for the past 20 years by the EPA to make our air cleaner basically have been lost in fire-prone areas and downwind regions,” Wang continued. “We are losing ground.”

To draw their conclusions, the scientists calculated nationwide concentration of both fine particulate matter (PM 2.5) and what they described as a “highly toxic” component of this air pollutant, known as “black carbon.”

They were particularly interested in mapping out levels of black carbon — a sooty material emitted via fossil fuel combustion — on a kilometer-by-kilometer across the continental U.S.

The scientists said they derived both the pollutant concentrations and premature death estimates from satellite data and 500 ground-based air quality monitoring stations.

Looking at the entire nation, the researchers observed that levels of PM 2.5 and black carbon decreased by 22 percent and 11 percent, respectively, from 2000-2020.

But since 2010, the authors found that the reverse was true for the U.S. West. This region has experienced a 55-percent annual increase in PM 2.5 concentrations and an 86 percent surge in black carbon levels, per the study.

The researchers also noticed sizable fluctuations in pollution levels from year-to-year, explaining that these shifts are “potentially attributable to the rising incidence of wildfires.”

Meanwhile, the proportion of PM 2.5 consisting of black carbon underwent “a notable annual increase of 2.4 percent across the U.S.” during the study period, which the authors attributed mainly to western wildfires.

When removing daily outliers linked to large fires, the scientists said they saw a significant decrease in overall PM 2.5 concentrations.

“The increasing number and intensity of wildfires in the U.S. counteract or even overshadow the reduction in anthropogenic emissions,” co-lead author Jing Wei, a postdoctoral scholar in Wang’s group during the study, said in a statement. 

These conditions are “exacerbating air pollution and heightening the risks of both morbidity and mortality,” added Wei, who is now assistant research scientist at the University of Maryland,

As opposed to the U.S., the eastern part of the country has experienced no major air quality declines from 2000-2020, according to the study.

Wildfires have affected the Midwest, on the other hand, but this region has thus far escaped direct health effects, the authors observed.

“We are on the borderline,” Wang said. “If fires increase or become more frequent, our air quality will get worse.”