Chart showing composition of reactive nitrogen species in wildfire smoke at different locations
Composition of reactive nitrogen species in wildfire smoke. Each bar denotes a wildfire plume sampled by a research aircraft which flew over wildfire smoke in the Western US during the summer of 2018. A key finding is that reduced nitrogen species (red portions of each bar) comprise a significant fraction of the total versus oxidized forms (all other colors). The ratio across wildfires depends on the modified combustion efficiency of the wildfire. Credit: Lindaas et al. [2021], Figure 2b
Source: Journal of Geophysical Research: Atmospheres

Wildfires are becoming an increasingly significant source of air pollution in the Western United States yet predicting the formation of secondary pollutants (such as ozone and aerosols) remains challenging due to uncertainties in emissions, chemical processes, and variability in burn conditions. Simply, how does one characterize emissions from “1000 small fires all burning differently”? (Jack Dibb, personal communication).

To address this problem, Lindaas et al. [2021] perform a comprehensive analysis of the NSF-sponsored Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN) field study. During WE-CAN, a research aircraft sampled 23 wildfires throughout the western United States in the summer of 2018. The researchers found that reduced nitrogen comprises a greater fraction relative to oxidized than previously thought, which is expected to alter the chemistry of wildfire smoke. The in-situ analysis provides insights that can lead to improvements in weather-chemistry models that predict ozone and fine particle formation downwind of large wildfires.

Citation: Lindaas, J., Pollack, I. B., Garofalo, L. A., Pothier, M. A., Farmer, D. K., Kreidenweis, S. M., et al. [2021]. Emissions of reactive nitrogen from Western U.S. wildfires during summer 2018. Journal of Geophysical Research: Atmospheres, 126, e2020JD032657.

—Brian McDonald, Associate Editor, JGR: Atmospheres

Text © 2021. The authors. CC BY-NC-ND 3.0
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