Photochemical evolution of the 2013 California Rim Fire: synergistic impacts of reactive hydrocarbons and enhanced oxidants

Abstract. Large wildfires influence regional atmospheric composition, but chemical complexity challenges model predictions of downwind impacts. Here, we elucidate key connections within gas-phase photochemistry and assess novel processes via a case study the 2013 California Rim Fire plume. Airborne in situ observations, acquired during NASA Studies Emissions, Atmospheric Composition, Clouds Climate Coupling by Regional Surveys (SEAC4RS) mission, illustrate evolution volatile organic compounds (VOCs), oxidants, reactive nitrogen over 12 h aging. Measurements show rapid formation ozone peroxyacyl nitrates (PNs), sustained peroxide production, prolonged enhancements oxygenated VOCs oxides (NOx). Observations Lagrangian trajectories constrain 0-D puff that approximates plume photochemical history provides framework for evaluating process interactions. Simulations examine effects (1) previously unmeasured identified recent laboratory studies (2) emissions secondary production nitrous acid (HONO). Inclusion estimated leads to 250 % increase OH reactivity 70 radical VOC photolysis. HONO amplifies cycling serves as NOx source, although impacts depend on how is introduced. The addition initial (representing primary emissions) or particulate nitrate photolysis while heterogeneous conversion NO2 suppresses formation. Analysis initiation rates suggests major exceeding when averaged first 2 Ozone chemistry transitions from sensitive hour aging, with both contributing significantly termination. To simulate smoke accurately, models should simultaneously account full pool all relevant oxidant sources.