Wildfires create much more pollution than previously thought

Georgia Tech had instruments and scientists on the NASA DC-8 plane. Researchers associated with a total of more than a dozen universities and organizations participated in data collection or analysis. The scientists published their findings on June 14 in the Journal of Geophysical Research: Atmospheres.

“This paper is expected to serve as a basis for the next NASA fire chemical monitoring mission,” Huey said.

Refinery in flames
Methanol, benzene, ozone precursors and other noxious emissions collected from wildfire plumes may make it sound like an oil refinery went up in flames. That’s not so far-fetched, as oil and other fossil fuels derive from ancient biomass.

“You can see the smoke, and it’s dark for a reason,” Huey said. “When you go measuring wildfires, you get everything there is to measure. You start to wonder sometimes what all is in there.”

The study found many organic chemicals in the wildfire plumes, and technological advancements allowed them to detect certain nitrates in the smoke for the first time. But burning biomass does not appear to be a dominant source of these chemical pollutants.

The major findings of the study involved the fine particles, which are dusty, sooty particles much thinner than a grain of sand or a human hair. They can go airborne, as aerosols, on their own or combined with moisture.

Then people can inhale them. Some particulate matter contains oxidants that cause genetic damage. They can drift over long distances and pollute populated areas.

Industrial sources also expose people to harmful aerosols, but fires produce more aerosol per amount of fuel burned. “Cars and power plants with pollution controls burn things much more cleanly,” Huey said.

Various aerosols also rise up in the atmosphere, but their net effect on global warming or cooling is still uncertain, as some aerosols reflect sunlight away from the Earth, and others, in contrast, trap warmth in the atmosphere.

Prescribed burnings
As global warming expands wildfires in size and number, the ensuing pollution stands to grow along with them. Stepping up professionally controlled man-made burnings may help cut these emissions, the study suggests.

So-called prescribed burnings prevent or reduce wildfires, and they appear to produce far less pollution per unit area than wildfires.

“A prescribed fire might burn five tons of biomass fuel per acre, whereas a wildfire might burn 30,” said Yokelson, who has dedicated decades of research to biomass fires. “This study shows that wildfires also emit three times more aerosol per ton of fuel burned than prescribed fires.”

While still more needs to be known about professional prescribed burnings’ emissions, this new research makes clear that wildfires burn much more and pollute much more. The data will also help improve overall estimates of wildfire emissions.

Fire prevention professionals follow stringent rules to carry out prescribed burns to avoid calamity and sending pollution downwind into populated areas. The researchers do not recommend that inexperienced people burn biomass, as this contributes to air pollution and can trigger tragic blazes, including wildfires.

Daunting flights
Experiments like these, in real natural disasters, are uncommon not only because of the challenge of assembling so many great instruments and taking them airborne. The flights are also potentially dangerous. Plumes are not only filled with toxins, but their turbulence tosses planes about, rattling technology and researchers.

“The smoke leaks into the cabin and makes you nauseous,” said Yokelson, who started flying plume missions many years ago. “You’re trying to take notes, run your instrument, look at the fire, talk on the headset, and get pictures. And at the same time, it’s crazy bumpy. Normally, if you’re in a smaller plane, your stomach is not too happy.”

Also, wildfires pop up unannounced, so flight schedules must be hammered out on short notice around strict regulations that normally prohibit flights near wildfires. Research aircraft also have to coordinate with regional authorities to avoid crossing paths with fire-fighting planes.

The rare data the flights from NASA’s SEAC4RS mission and the Department of Energy’s BBOP mission have provided stand to greatly increase understanding of the pollutants naturally burning biomass flings into the air.

— Read more in Xiaoxi Liu et al., “Airborne measurements of western U.S. wildfire emissions: Comparison with prescribed burning and air quality implications,” Journal of Geophysical Research: Atmospheres (14 June 2017) (DOI: 10.1002/2016JD026315)