Responses of Secondary Inorganic Aerosols to Synergistic NOx 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 NOx−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 NOx 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 NOx 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 NOx and NH3 control is the most effective strategy, reducing PNO3− and PNH4+ concentrations by 2.27 ug/m3 and 0.77 ug/m3, respectively.