Responses of Secondary Inorganic Aerosols to Synergistic NO_x and NH₃ Emission Control Based on an Inversion Inventory

Secondary inorganic aerosols (SIAs) are critical components of regional air pollution, yet uncertainties in bottom-up emission inventories lead to biases in the simulation of nitrate (PNO₃^-) and ammonium (PNH₄⁺). This study utilizes a joint NO_x-NH₃ inversion inventory constrained by satellite observations to investigate the response characteristics of SIAs to precursor reductions in the Beijing-Tianjin-Hebei (BTH) region during July 2020. Results indicate that the a priori emission inventory significantly underestimated NH₃ emissions in the BTH region, with a posteriori emission in cities such as Shijiazhuang and Handan increasing to 2-3 times the a priori levels, while NO_x emissions were slightly underestimated. Sensitivity analysis conducted via Comprehensive Air Quality Model with extensions (CAMx)-Decoupled Direct Method (DDM) reveals that the sensitivities of PNO₃^- and PNH₄⁺ to precursor variations are higher in south-central BTH; specifically, the sensitivity of PNO₃^- concentration to NO_x emission abatement under the a posteriori inventory rises substantially compared with a priori estimates, with relative growth rates spanning 33% to 308% across the study domain. Scenario simulations demonstrate that synergistic NO_x and NH₃ control is the most effective strategy, reducing PNO₃^- and PNH₄⁺ concentrations by 2.27 ug/m³ and 0.77 ug/m³, respectively.