Distance-dependent and nonlinear PM2.5 exposure responses to precursor-specific emission controls across Northeast Asia

Despite extensive emission control efforts, PM_2.5 concentrations in Northeast Asia remain well above national standards and World Health Organization guidelines, posing persistent public health challenges. This study aims to identify the precursors and source regions that effectively reduce both PM_2.5 concentrations and population exposure across Northeast Asia. Using a comprehensive chemical transport model and 25 precursor-specific emission reduction scenarios, we systematically evaluated the effectiveness of emission controls on PM_2.5 concentrations and population-weighted concentrations (PWCs) across multiple spatial scales. For a 50% nationwide reduction of pollutants in China, PM_2.5 concentrations decreased by 15.9, 7.7, and 2.8 μg/m³ in China, South Korea, and Japan, respectively; meanwhile, PWCs declined by 22.7, 8.2, and 2.5 μg/m³, respectively. Among individual precursors, NO_X and NH₃ exhibited the broadest regional influences through secondary aerosol formation, whereas controls targeting primary PM_2.5 produced strong but localized benefits. Under complete emission elimination, NO_X became the dominant control variable, lowering PWCs by 28.9 μg/m³ in China and 10.3 μg/m³ in South Korea—surpassing the benefits of eliminating primary PM_2.5 emissions. Distance-dependent analyses revealed that NO_X and NH₃ effects persisted over approximately 1100–1400 km downwind, defined by the 50% decay distance of maximum PM_2.5 impacts, encompassing more than one billion people in densely populated receptor regions such as Seoul and Shanghai. These results highlight the importance of regionally coordinated mitigation strategies that prioritize precursors with high exposure efficiency, by explicitly accounting for precursor-specific nonlinearity, distance-dependent transport, and population exposure across multiple spatial scales. Integrating concentration- and exposure-based indicators within joint NO_X–NH₃ control frameworks can substantially enhance the equity and effectiveness of PM_2.5 management across Northeast Asia.