Evaluating Oxidant Field Representations in Aerosol Modeling: Insights from the ASIA-AQ Campaign and Global Budgets

Abstract. Accurate prediction of secondary inorganic aerosols (e.g., sulfate and nitrate) relies heavily on representing highly variable, nonlinear atmospheric oxidant chemistry. This study systematically evaluates the sensitivity of GOCART-2G aerosol simulations to the temporal resolution and underlying chemical mechanisms of three oxidant fields: hourly GEOS-Chem (CFH), monthly GEOS-Chem (CFM), and monthly GMI-Chem climatology (GMI). Model performance was assessed using airborne data from the 2024 ASIA-AQ campaign (covering the Philippines, South Korea, and Thailand) and global simulations for 2019. Comparisons show that hourly, time-varying oxidant fields improve simulated oxidant, sulfate, and nitrate correlations over monthly averages. Capturing short-term variability—particularly the strong diurnal cycles of OH and NO3—preserves the temporal covariance and nonlinear coupling that monthly means obscure. Consequently, time-resolved oxidants weaken the overall chemical transformation of dimethyl sulfide (DMS). This results in ~20 % higher global DMS and methanesulfonic acid (MSA) burdens than monthly mean simulations, while exerting substantial regional impacts (>20 %) on sulfur and nitrate budgets over East Asia. Furthermore, variations in monthly mean oxidant magnitude and spatial distribution between GMI-Chem and GEOS-Chem mechanisms impact aerosol burdens. GMI-Chem produces 2 % and 8 % higher column and surface sulfate, respectively, but 148 % and 130 % lower column and surface nitrate. These findings highlight the limitations of decoupled, time-averaged oxidant fields in traditional global models, demonstrating that resolving high-frequency temporal variability and nonlinear feedbacks is critical for Earth System Models.