Fire Emissions Pose Health Threats Hundreds of Miles from the Flames

A new model by researchers in Carnegie Mellon University’s College of Engineering shows that health hazards from fires go beyond the burned areas, and fire emissions can contribute to cardiovascular disease hundreds of miles from the flames. The researchers said the risks are greater and more widespread than most predictive models show.

Spyros Pandis, professor of chemical engineering, warned that people downwind of a fire are not fully anticipating its possible effects on their health.

“The evidence suggests that these emissions are just as bad for our health as that of other combustion sources, such as vehicle and industrial emissions,” Pandis said. “The emissions from wildfires contain thousands of complex organic compounds, some of them carcinogenic.”

The emissions in question are biomass burning organic aerosols, which originate from burning plants, trees and other organic matter. Pandis, along with Allen Robinson, head and professor of mechanical engineering; and Laura Posner — who graduated with a doctorate in chemical engineering — created a 3D model of biomass burning organic aerosols to track two types: primary organic aerosols and secondary organic aerosols. Their work was published in the journal Atmospheric Environment.

Primary organic aerosols are emitted directly into the atmosphere from the fire in the particle phase and are mostly concentrated within a fire’s vicinity. Secondary organic aerosols consist of organic vapor emissions that condense in the particle phase after burning and spread out further. Most computer models that track particle movement in the air after a fire track primary emissions and ignore secondary emissions.

For the new model, the team entered data from across the U.S. from three months of 2008, creating a set of predictions that they then checked against historic data from aerosol tracking networks and predictions from a model focused only on primary organic aerosols.

The researchers studied April, when controlled agriculture fires boosted emissions; and July and September, when wildfires were most common.

Taking secondary organic aerosols into account, the researchers’ model predicted significantly higher average concentration values of biomass burning organic aerosols than less-sophisticated models — 66 percent higher in April and a little more than 100 percent higher in July and September. The CMU researchers’ model was more accurate when compared to actual measurements. They also showed that the secondary organic aerosols previously were underestimated.

“Atmospheric chemistry acts as a booster,” Pandis said, “producing additional particulate matter as the plume moves away from the fire one or two days later. The effects, of course, get smaller as one gets away from the fire, but it can remain significant up to 600 miles away — even if it’s no longer visible as thick smoke. This enhancement is stronger during warm sunny days.”

Wildfires decimated 8.8 million acres in the United States in 2018, on a sharp curve up from a little more than 2 million in 1985, according to the National Interagency Fire Service.

The authors said they hope that this research will help expand the public’s understanding of the severity of these wildfires and the importance of limiting them in the future.

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