Fires could emit more air pollution than previously estimated

(Press-News.org) As fires burn the landscape, they spew airborne gases and particles, though their impact on air pollution might be underestimated. A study in ACS’ Environmental Science & Technology reports that, around the world, wildfires and prescribed burns (i.e., wildland fires) could emit substantially more gases, including ones that contribute to air pollution, than previously thought. The researchers identified several regions with high wildland fire and human activity emissions, which may pose complex air-quality challenges.

“Our new estimates increase the organic compound emissions from wildland fires by about 21%,” says Lyuyin Huang, the first author of the study. “The inventory provides a foundation for more detailed air-quality modeling, health-risk assessment and climate-related policy analysis.”

Each year, large swaths of forests, grass and peat burn in wildfires, releasing a complex mix of water vapor, ash and carbon-based compounds into the air. Some of these carbon-based compounds are gases called volatile organic compounds (VOCs). Others that evaporate and turn into gases at warmer temperatures are known as intermediate- and semi-volatile organic compounds (IVOCs and SVOCs, respectively). And in the air, these partially-volatile compounds form fine particles — pollutants that can be harmful if breathed in — more easily than VOCs. However, most studies assessing wildland fire emissions overlook IVOCs and SVOCs because of their large number, which makes it hard to measure these compounds. Researchers led by Shuxiao Wang wanted to take IVOCs and SVOCs emissions along with VOCs into consideration to offer better insight into wildland fires’ impact on air quality, health and climate.

First, the researchers accessed a database of the burned land area for global forest, grass and peatland wildland fires from 1997 to 2023. They also collected data on the VOCs, IVOCs, SVOCs, and other extremely low volatility organic compounds emitted as each vegetation type burns. For vegetation types without field measurements, they relied on laboratory experiments to predict the organic compounds released. Then, the team combined these datasets and calculated annual emissions around the world.

Altogether, the researchers estimated wildland fires released an average of 143 million tons of airborne organic compounds each year of the study. This amount is 21% higher than earlier estimates, suggesting that wildland fire emissions, specifically the IVOCs and SVOCs, could cause more air pollution than previously thought.

Comparing wildland fire emissions to their earlier estimate of human activities that release airborne compounds, the researchers found that the human-caused emissions were greater overall, but both sources released equivalent amounts of IVOCs and SVOCs. Additionally, multiple emission hotspots for both wildfire and human activity emerged from the comparison: Equatorial Asia, Northern Hemisphere Africa and Southeast Asia. The researchers say these regions’ air pollution challenges are complex, requiring different strategies to reduce emissions from fires and human activities.

The authors acknowledge funding from the National Natural Science Foundation of China, National Key R&D Program of China, the Samsung Advanced Institute of Technology, and the Center of High Performance Computing at Tsinghua University.

The paper’s abstract will be available on Dec. 29 at 8 a.m. Eastern time here: http://pubs.acs.org/doi/abs/10.1021/acs.est.5c10217

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