For many years, Beijing has suffered from severe air pollution. At present, fine particulate matter (PM_2.5) pollution in the winter and ozone (O₃) pollution in the summer constitute serious environmental problems. In this study, the combination of a comprehensive air quality model with particulate matter source apportionment technology (CAMx-PAST) and monitoring data was used for the high-spatial resolution source apportionment of secondary inorganic components (SNA: SO₄²⁻, NO₃⁻, and NH₄⁺) in PM_2.5; their corresponding precursor gases (SO₂, NO₂, and NH₃); and O₃ in the winter and summer over Beijing. Emissions from residents, industry, traffic, agriculture, and power accounted for 54%, 25%, 14%, 5%, and 2% of PM_2.5 in the winter, respectively. In the summer, the emissions from industry, traffic, residents, agriculture, and power accounted for 42%, 24%, 20%, 10%, and 4% of PM_2.5, respectively. The monthly transport ratio of PM_2.5 was 27% and 46% in the winter and summer, respectively. The regional transport of residential and industrial emissions accounted for the highest proportion of PM_2.5. The regional transport of emissions had a significant effect on the SO₄²⁻ and NO₃⁻ concentrations, whereas SO₂ and NO₂ pollution were mainly affected by local emissions, and NH₄⁺ and NH₃ were mainly attributed to agricultural emissions. Industrial and traffic sources were two major emission sectors that contributed to O₃ pollution in Beijing. The monthly transport ratios of O₃ were 31% and 65% in the winter and summer, respectively. The high-spatial resolution regional source apportionment results showed that emissions from Langfang, Baoding, and Tangshan had the greatest impact on Beijing’s air pollution. This work’s methods and results will provide scientific guidance to support the government in its decision-making processes to manage the PM_2.5 and O₃ pollution issues.

The influence of sub-grid particle formation (SGPF) in point source plumes on aerosol particles over eastern China was firstly illustrated by implementing a SGPF scheme into a global-regional nested chemical transport model with aerosol microphysics module. The key parameter in the scheme was optimized based on the observations in eastern China. With the parameterization of SGPF, the spatial heterogeneity and diurnal variation of particle formation processes in sub-grid scale were well resolved. The SGPF scheme can significantly improve the model performance in simulating aerosol components and new particle formation processes at typical sites influenced by point sources. The comparison with observations at Beijing, Wuhan, and Nanjing showed that the normal mean bias (NMB) of sulfate and ammonium could be reduced by 23%-27% and 12%-14%, respectively. When wind fields were well reproduced, the correlation of sulfate between simulation and observation can be increased by 0.13 in Nanjing. Considering the diurnal cycle of new particle formation, the SGPF scheme can greatly reduce the overestimation of particle number concentration in nucleation and Aitken mode at night caused by fixed-fraction parameterization of SGPF. In the regional scale, downwind areas of point source got an increase of sulfate concentration by 25%-50%. The results of this study indicate the significant effects of SGPF on aerosol particles over areas with the point source and necessity of reasonable representation of SGPF processes in chemical transport models.