Biomass Burning Plume Chemistry via Iodide-Adduct Chemical Ionization Mass Spectrometry: Secondary Organic Aerosol Formation and Reactive Nitrogen Evolution

Biomass burning emissions and chemistry were measured using iodide-adduct ionization time-of-flight chemical ionization mass spectrometry (I^- CIMS) on the National Science Foundation (NSF) / National Center for Atmospheric Research (NCAR) C-130 aircraft platform during the Western wildfire Experiment for Cloud chemistry, Aerosol absorption and Nitrogen (WE-CAN) 2018 field campaign in the Western United States. The iodide reagent anion clusters with a wide range of analyte gas-phase molecules that are important in biomass burning emissions, including inorganic nitrogen and sulfur (HNO₃, HONO, N₂O₅, SO₂, etc.), a broad suite of oxidized organic molecules (C_xH_yO_z), and a variety of organic nitrogen species (HCN, HNCO, C_xH_yO_zN_w, etc.). Halogen chemistry in smoke plumes can also be investigated (e.g., ClNO₂, HOCl, etc.). In conjunction with other instrumentation including aerosol and gas-phase measurements (e.g., PM₁, NO_x, VOC's), wildfires were sampled at a range of distances from the fires with the intent to characterize the chemical evolution of the plumes. Both individual plume analyses and statistical analyses of plumes across the variety of fuel types and fire characteristics will be presented. Specific analyses will focus on the evolution of reactive nitrogen in the plume, and on secondary organic aerosol (SOA) formation from a molecular composition perspective. Previous research has demonstrated that aging of biomass burning plumes in the atmosphere can exhibit a range of SOA formation behavior, including net SOA formation, net SOA loss, or no change. The reasons for this behavior are not well understood, in part because of the chemical complexity and variability of biomass burning emissions. Using the I^- CIMS, I will survey the composition and variability of oxidized organic/nitrogen gases in the smoke. These molecules can be constituents of SOA and/or react to form SOA directly. Combined with supporting measurements, I will present initial findings of I^- CIMS insights into SOA formation in wildfire smoke.