Emissions of Reactive Nitrogen From Western U.S. Wildfires During Summer 2018

Jakob Lindaas, Ilana B. Pollack, Lauren A. Garofalo, Matson A. Pothier, Delphine K. Farmer, Sonia M. Kreidenweis, Teresa L. Campos, Frank Flocke, Andrew J. Weinheimer, Denise D. Montzka, Geoffrey S. Tyndall, Brett B. Palm, Qiaoyun Peng, Joel A. Thornton, Wade Permar, Catherine Wielgasz, Lu Hu, Roger D. Ottmar, Joseph C. Restaino, Andrew T. HudakI. Ting Ku, Yong Zhou, Barkley C. Sive, Amy Sullivan, Jeffrey L. Collett, Emily V. Fischer

Research output: Contribution to journalArticlepeer-review

48 Scopus citations

Abstract

Reactive nitrogen (Nr) 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 Nr normalized excess mixing ratios and emission factors from fires sampled within 80 min of estimated emission and explore variability in the dominant forms of Nr between these fires. We find that reduced N compounds comprise a majority (39%–80%; median = 66%) of total measured reactive nitrogen (ΣNr) 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 (ΣNOy) and measured total ΣNHx (NH3 + pNH4) are more robustly correlated with modified combustion efficiency (MCE) than NOx and NH3 by themselves. The ratio of ΣNHx/ΣNOy displays a negative relationship with MCE, consistent with previous studies. A positive relationship with total measured ΣNr suggests that both burn conditions and fuel N content/volatilization differences contribute to the observed variability in the distribution of reduced and oxidized Nr. Additionally, we compare our in situ field estimates of Nr EFs to previous lab and field studies. For similar fuel types, we find ΣNHx EFs are of the same magnitude or larger than lab-based NH3 EF estimates, and ΣNOy EFs are smaller than lab NOx EFs.

Original languageEnglish
Article numbere2020JD032657
JournalJournal of Geophysical Research: Atmospheres
Volume126
Issue number2
DOIs
StatePublished - Jan 27 2021

Keywords

  • ammonia
  • emissions
  • nitrogen oxides
  • reactive nitrogen
  • wildfire smoke

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