Measured and Modeled Ozone Production and Photochemistry in Biomass Burning Smoke in Rural Idaho

Abstract:

Although ozone (O₃) is not directly emitted from biomass burning (BB), it can form in BB plumes by photochemical reactions involving volatile organic compounds, nitrogen oxides, and ROx (OH, HO₂, and RO₂) precursors, many of which are emitted directly by BB. Our understanding of the impact of biomass burning on ozone is limited by our understanding of the underlying radical chemistry. Measurements of any ROx species in BB smoke, however, are extremely rare. We present results from a 2018 field campaign in rural McCall, Idaho in which we characterized the chemical composition, including peroxy radical concentrations, of air occasionally impacted by smoke from different wildfires. Enhancements in both ozone and peroxy radical concentrations were observed for some BB plumes, including one sampled air mass in which ozone and peroxy radical concentrations increased by ~15 ppb and ~15 ppt, respectively, compared to background air. Instantaneous ozone production (P(O₃)) rates were calculated using these peroxy radical measurements. Median P(O₃) rates peaked at ~5 ppb hr^-1 due to low background NOx concentrations (typically ~0.1 ppbv NO) with minimal enhancements from biomass burning. We also present comparisons of peroxy radical concentrations measured by our ECHAMP sensor and predicted by zero-dimensional models using the Master Chemical Mechanism.