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Atmospheric fine particulate pollution has been a dramatically environmental concern in all seasons in the megacity Beijing in recent years. A long-term real-time monitoring campaign of non-refractory submicron aerosol (NR-PM 1) at a southeastern urban site in Beijing from July 13, 2017 to May 26, 2018 using an Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was carried out to investigate the characteristics and evolution processes of NR-PM 1 and its potential source effects. The annual average concentration of NR-PM 1 during the entire study period was 40.8 μg/m3, lower than that of NR-PM 1 from July 2011 to June 2012, and its seasonal variation presented the order of autumn and spring > winter > summer. The average concentration of organic species Org in the entire study was 15.1 μg/m3 and accounted for 37% of NR-PM 1 , being consistently a significant component of NR-PM 1 in the four seasons. The average concentrations of SO 4 2− and NO 3 − were 8.6 and 11.1 μg/m3, respectively, accounting for 21% and 27% of NR-PM 1 , and NO 3 − and its contribution to NR-PM 1 exceeded those of SO 4 2−, suggesting that secondary nitrate became a more dramatic pollutant. Note that SO 4 2− in summer accounted for 27% of NR-PM 1 , higher than those in the other seasons, indicating that secondary sulfate formation was greatly important in summer, however, NO 3 − in summer accounted for 22% of NR-PM 1 , lower than those in the other seasons, more likely due to relatively high temperature in summer being favorable for dissociation of nitrate. NH 4 + and Cl− species presented lower mass concentrations and mass fractions, and the seasonal variation of NH 4 + was similar to NO 3 −, yet Cl− presented a typical seasonal change related to intense fossil fuel combustion during the heating period in winter and biomass burning in autumn with an order of winter > autumn > spring > summer. All aerosol species exhibited different diurnal cycles, of which Org presented a bimodal mode, SO 4 2− and Cl− showed a flatter diurnal pattern, however, NO 3 − and NH 4 + displayed more similar single-peak patterns. The conversion of SO 2 to SO 4 2− presented an obvious seasonal variation with summer > autumn > spring > winter driven by different factors. The conversion of NO 2 to NO 3 − also showed a significant seasonal change characterized by autumn > summer and spring > winter controlled by different factors. Relative humidity, temperature and wind speed during the study period were significant meteorological elements influencing NR-PM 1 and its species, and heavy haze pollution episodes largely occurred under high relative humidity and low wind speed. High potential source regions influencing NR-PM 1 pollution in Beijing in all seasons presented dramatically distributions related to wind directions. • The mean loadings of all NR-PM 1 species in the entire study followed the order of Org > NO 3 − > SO 4 2− > NH 4 + > Cl−. • All NR-PM 1 species obviously presented different seasonal variations. • RH and NH 3 could promote the conversions of SO 2 to SO 4 2− and NO 2 to NO 3 −in all seasons. • High potential source regions influencing Beijing NR-PM 1 showed distinct distributions related to wind directions. [ABSTRACT FROM AUTHOR]