HONO Emissions from Western U.S. Wildfires Provide Dominant Radical Source in Fresh Wildfire Smoke

Qiaoyun Peng, Brett B. Palm, Kira E. Melander, Ben H. Lee, Samuel R. Hall, Kirk Ullmann, Teresa Campos, Andrew J. Weinheimer, Eric C. Apel, Rebecca S. Hornbrook, Alan J. Hills, Denise D. Montzka, Frank Flocke, Lu Hu, Wade Permar, Catherine Wielgasz, Jakob Lindaas, Ilana B. Pollack, Emily V. Fischer, Timothy H. BertramJoel A. Thornton

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


Wildfires are an important source of nitrous acid (HONO), a photolabile radical precursor, yet in situ measurements and quantification of primary HONO emissions from open wildfires have been scarce. We present airborne observations of HONO within wildfire plumes sampled during the Western Wildfire Experiment for Cloud chemistry, Aerosol absorption and Nitrogen (WE-CAN) campaign. Î"HONO/Î"CO close to the fire locations ranged from 0.7 to 17 pptv ppbv-1 using a maximum enhancement method, with the median similar to previous observations of temperate forest fire plumes. Measured HONO to NOx enhancement ratios were generally factors of 2, or higher, at early plume ages than previous studies. Enhancement ratios scale with modified combustion efficiency and certain nitrogenous trace gases, which may be useful to estimate HONO release when HONO observations are lacking or plumes have photochemical exposures exceeding an hour as emitted HONO is rapidly photolyzed. We find that HONO photolysis is the dominant contributor to hydrogen oxide radicals (HOx = OH + HO2) in early stage (<3 h) wildfire plume evolution. These results highlight the role of HONO as a major component of reactive nitrogen emissions from wildfires and the main driver of initial photochemical oxidation.

Original languageEnglish
Pages (from-to)5954-5963
Number of pages10
JournalEnvironmental Science and Technology
Issue number10
StatePublished - May 19 2020


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