Quantification of organic aerosol and brown carbon evolution in fresh wildfire plumes

Brett B. Palm, Qiaoyun Peng, Carley D. Fredrickson, Ben H. Lee, Lauren A. Garofalo, Matson A. Pothier, Sonia M. Kreidenweis, Delphine K. Farmer, Rudra P. Pokhrel, Yingjie Shen, Shane M. Murphy, Wade Permar, Lu Hu, Teresa L. Campos, Samuel R. Hall, Kirk Ullmann, Xuan Zhang, Frank Flocke, Emily V. Fischer, Joel A. Thornton

Research output: Contribution to journalArticlepeer-review

107 Scopus citations


The evolution of organic aerosol (OA) and brown carbon (BrC) in wildfire plumes, including the relative contributions of primary versus secondary sources, has been uncertain in part because of limited knowledge of the precursor emissions and the chemical environment of smoke plumes. We made airborne measurements of a suite of reactive trace gases, particle composition, and optical properties in fresh western US wildfire smoke in July through August 2018. We use these observations to quantify primary versus secondary sources of biomass-burning OA (BBPOA versus BBSOA) and BrC in wildfire plumes. When a daytime wildfire plume dilutes by a factor of 5 to 10, we estimate that up to onethird of the primary OA has evaporated and subsequently reacted to form BBSOA with near unit yield. The reactions of measured BBSOA precursors contribute only 13 ± 3% of the total BBSOA source, with evaporated BBPOA comprising the rest. We find that oxidation of phenolic compounds contributes the majority of BBSOA from emitted vapors. The corresponding particulate nitrophenolic compounds are estimated to explain 29 ± 15% of average BrC light absorption at 405 nm (BrC Abs405) measured in the first few hours of plume evolution, despite accounting for just 4 ± 2% of average OA mass. These measurements provide quantitative constraints on the role of dilution-driven evaporation of OA and subsequent radical-driven oxidation on the fate of biomass-burning OA and BrC in daytime wildfire plumes and point to the need to understand how processing of nighttime emissions differs.

Original languageEnglish
Pages (from-to)29469-29477
Number of pages9
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number47
StatePublished - Nov 24 2020


  • Aircraft measurements
  • Biomass burning
  • Brown carbon
  • Phenolic compounds
  • Secondary organic aerosol


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