Simulation Of The Characteristics And Precursor Emission Control Of Water-soluble Inorganic Aerosols

Sulfate, nitrate, and ammonium（simplified as SNA） are predominant water-soluble inorganic species of PM_2.5. In this study, the GEOS-Chem chemical transport model is used to simulate SNA aerosols over China, and it is improved to perform better in simulating the extremely high concentration and characteristics of SNA during heavy polluted period in China. We use the improved GEOS-Chem model to simulate the chemical composition, concentration level and distribution of SNA over China and investigate the response of SNA to precursor emission changes, to evaluate the current SO₂ and NOX emission control policy and give implications for future emission control strategy.On seasonal and annual mean level, the GEOS-Chem model is proved to have good skill in reproducing the spatial and temporal distribution of PM_2.5 and SNA, with some bias in simulating the concentration level. During the heavy polluted period, the model underestimates sulfate concentration by several folds and cannot capture sulfate fraction increase in PM_2.5, we improve model’s performance by adding the heterogeneous reaction of SO₂ on wet aerosol into the chemical module, making it capable to simulate the characteristic of sulfate in heavy polluted period, and partly solved the overestimation of nitrate concentration in the model.The seasonality of SNA over North China（NC） is determined mainly by the chemical formation rate of each species, while those over South China（SC） and Southwest China（SWC） are influenced by the seasonality of precursor emissions and the wet deposition.Changes of SNA over China from 2000 to 2015 are determined by precursor emissions. From 2000 to 2006, Chinese SO₂ and NOX emission has increased by 60% and 80%, respectively, resulting in a 50% increase of mean SNA concentration. From 2006 to 2015, SO₂ and NOX emission control is effective in controlling SNA concentrations, but NOX emission abatement should be strengthened in NC and SC. NH3 emission also has significant influence on SNA aerosols. From 2006 to 2015, increase of NH3 emission will offset the effect of SO₂ and NOX control; and in the future, if NH3 emission decreases besides SO₂ and NOX emission control, the percent of SNA concentration decrease will be doubled.The SO₂ emission control efficiency（defined as relative change of impact metric due to 1% SO₂ emission reduction） differs from region to region. With the same amount of emission reduction, SO₂ control over NC is the most effective in reducing national mean surface sulfate concentration, and SO₂ emission control over SC is most effective in reducing people’s exposure to sulfate aerosols. In addition, NC makes the largest contribution to interregional transport of sulfur within China and to the transport fluxes to Western Pacific. China needs to carefully design a regionally specific implementation plan of realizing its SO₂ emissions reduction target in order to maximize the resulting air quality benefits not only for China but for the downwind regions, with emphasis on reducing emissions from NC.