Aerosols from Fires: An Examination of the Effects on Ozone Photochemistry in the Western United States

摘要

This study presents a first attempt to investigate the roles of fire aerosols in ozone (O_3) photochemistry using an online coupled meteorology-chemistry model, the Weather Research and Foresting model with Chemistry (WRF-Chem). Four 1-month WRF-Chem simulations for August 2007, with and without fire emissions, were carried out to assess the sensitivity of O_3 predictions to the emissions and subsequent radiative feedbacks associated with large-scale fires in the Western United States (U.S.)- Results show that decreases in planetary boundary layer height (PBLH) resulting from the radiative effects of fire aerosols and increases in emissions of nitrogen oxides (NO_x) and volatile organic compounds (VOCs) from the fires tend to increase modeled O_3 concentrations near the source. Reductions in downward shortwave radiation reaching the surface and surface temperature due to fire aerosols cause decreases in biogenic isoprene emissions and J(NO_2) photolysis rates, resulting in reductions in O_3 concentrations by as much as 15%. Thus, the results presented in this study imply that considering the radiative effects of fire aerosols may reduce O_3 overestimation by traditional photochemical models that do not consider fire-induced changes in meteorology; implementation of coupled meteorology-chemistry models are required to simulate the atmospheric chemistry impacted by large-scale fires.