In Situ Measurements and Evaluation of Primary Radical Budgets within Wildfire Plumes during WE-CAN

Wildfires emit a wide variety of pollutants that influence tropospheric chemistry and deteriorate air quality. Radicals are abundantly formed in biomass burning plumes, and the interaction between radical formation and radical-initiated degradation plays an important role in the fate of many key chemical species. However, solid understanding of the processes involved is currently lacking. Smoke plumes from wildfires in the western United States were sampled from an instrumented NSF/NCAR C-130 aircraft during the Western wildfire Experiment for Cloud chemistry, Aerosol absorption and Nitrogen (WE-CAN) campaign in summer 2018. We use in-situ observations of O₃, HONO, HCHO, ClNO₂, among others measured using iodide-adduct chemical ionization mass spectrometry, together with actinic flux to assess primary radical production rates within wildfire plumes, which is important for providing further information on secondary pollutants formation and aging of trace gases. We compare radical forming potential with the dilution normalized decay rates of trace gases such as SO₂, NO₂, and their oxidation products, as well as organics such as isoprene and monoterpenes, to determine both an OH reactivity and effective OH concentration in near-source plumes. These constraints are used to interpret formation rates of ozone and secondary aerosol products and variability therein across the range of wildfire plumes sampled.