Emissions of reactive nitrogen from western U.S. wildfires during summer 2018

Abstract

Reactive nitrogen (N_r) within smoke plumes plays important roles in the production of ozone, the formation of secondary aerosols, and deposition of fixed N to ecosystems. The Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN) field campaign sampled smoke from 23 wildfires throughout the western U.S. during summer 2018 using the NSF/NCAR C-130 research aircraft. We empirically estimate N_r normalized excess mixing ratios and emission factors from fires sampled within 80 min of estimated emission and explore variability in the dominant forms of N_r between these fires. We find that reduced N compounds comprise a majority (39%–80%; median = 66%) of total measured reactive nitrogen (ΣN_r) emissions. The smoke plumes sampled during WE-CAN feature rapid chemical transformations after emission. As a result, within minutes after emission total measured oxidized nitrogen (ΣNO_y) and measured total ΣNH_x (NH₃ + pNH₄) are more robustly correlated with modified combustion efficiency (MCE) than NO_x and NH₃ by themselves. The ratio of ΣNH_x/ΣNO_y displays a negative relationship with MCE, consistent with previous studies. A positive relationship with total measured ΣN_r suggests that both burn conditions and fuel N content/volatilization differences contribute to the observed variability in the distribution of reduced and oxidized N_r. Additionally, we compare our in situ field estimates of N_r EFs to previous lab and field studies. For similar fuel types, we find ΣNH_x EFs are of the same magnitude or larger than lab-based NH₃ EF estimates, and ΣNO_y EFs are smaller than lab NO_x EFs.

Keywords

Reactive nitrogen, air quality, western wildfires, WE-CAN.

Citation

Lindaas, Jakob; Pollack, Ilana B.; Garofalo, Lauren A.; Pothier, Matson A.; Farmer, Delphine K.; Kreidenweis, Sonia M.; Campos, Teresa L.; Flocke, Frank; Weinheimer, Andrew J.; Montzka, Denise D.; Tyndall, Geoffrey S.; Palm, Brett B.; Peng, Qiaoyun; Thornton, Joel A.; Permar, Wade; Wielgasz, Catherine; Hu, Lu; Ottmar, Roger D.; Restaino, Joseph C.; Hudak, Andrew T.; Ku, I‐Ting; Zhou, Yong; Sive, Barkley C.; Sullivan, Amy; Collett, Jeffrey L.; Fischer, Emily V. 2021. Emissions of reactive nitrogen from western U.S. wildfires during summer 2018. Journal of Geophysical Research: Atmospheres. 126(2): 1341. https://doi.org/10.1029/2020JD032657.