Researchers improve ability to predict wildfire smoke impacts
A team of U.S. National Science Foundation-supported researchers discovered that incorporating a better representation of carbon-based chemicals found in smoke into advanced models enables more accurate predictions of air pollutants to help improve air quality.
The new study identified a set of volatile organic compounds (VOCs) in chemical transport models that improve the prediction of hydroxyl radicals, ozone and reactive nitrates, all of which can affect air pollution.
The work advances the understanding that these models, traditionally used to study urban or remote environments, can now better predict wildfire-driven air pollution.
Wildfires have consumed more land over the past 30 years, releasing increasing amounts of smoke into the atmosphere. In 2022, almost 69,000 wildfires burned 7.6 million acres across the U.S. The influx of smoke carries respiratory and other health risks to humans and impacts natural environments.
Flying into the fire
The team studied information collected during an NSF-supported field campaign called the Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption and Nitrogen (WE-CAN). During the campaign, researchers flew over more than 20 wildfires during the summer of 2018.
In addition to WE-CAN, the team also studied data collected by the Fire Influence on Regional to Global Environments and Air Quality , also known as FIREX-AQ, field campaign, jointly supported by the National Oceanic and Atmospheric Administration and NASA. The wildfires burned western U.S. forests that included ponderosa pine, Douglas fir, lodgepole pine and other species.
Discovering how fire evolves
Researchers analyzed data collected within the first five hours of plume formation. Ozone is produced rapidly in the first few hours of smoke growth, affecting reactive nitrogen levels and further influencing how ozone forms downwind.
The team designed an analysis to identify how ozone and VOCs, among other chemicals, form and evolve in wildfire smoke plumes. It then tested what's currently known in air quality models, finding that the chemical age better explains what's happening than the physical age.
Chemical ages largely depend on chemical reactions driven primarily by hydroxyl radicals (OH), while physical ages progress over time. Freshly emitted smoke can sustain unusually high OH levels, which accelerate VOC oxidation and effectively "age" the plume faster than expected based on physical age. As a result, two plumes of the same physical age can be at very different stages of chemical transformation.
With a clearer understanding of how wildfire smoke chemically evolves as it interacts with the atmosphere, the team is now working to scale these findings from individual plumes to regional or global levels.