Chemical species and organic aerosol (OA) sources of atmospheric non-refractory particulate matter (NR-PM) were compared between Beijing and Tianjin during warm seasons. Beijing exhibits superior PM_2.5 control efficacy, with consistently lower concentrations and better spatial uniformity than those in Tianjin. Tianjin shows higher concentrations of OA, nitrate, and ammonium. The secondary OA (SOA) composition differs significantly between the two cities. Tianjin suffers severer photochemical pollution with higher O₃ and oxidant levels, revealing stronger atmospheric oxidation capacity. Beijing’s dominant wind directions feature alternating northerly and southerly winds, while Tianjin is characterized by persistent easterly and southerly flows. This difference in wind patterns results in a 5-h disparity in the diurnal peak timing of NR-PM_2.5 between the two cities. Additionally, compositional and meteorological differences lead to distinct pollution formation mechanisms. Tianjin shows pronounced nocturnal accumulation of primary emissions, while Beijing demonstrates more stable nighttime levels. Source analysis highlights Beijing’s effective vehicle emission control despite its larger vehicle fleet. Tianjin’s peak hourly increase rate of COA is 1.8 times Beijing’s in spring but only 0.4 times in summer. Sharing control experience and co-developing a real-time, high-resolution “cooking-traffic” emission inventory will help both cities refine source-specific controls. Both cities face PM_2.5-O₃ co-pollution challenges, more severe in Tianjin, with secondary inorganic aerosols dominating during high pollution episodes. Furthermore, our results underscore the necessity for enhanced regional collaborative governance to combat secondary pollution. Pollutants transport to Tianjin are dominated by southerly and easterly transport, whereas Beijing is primarily influenced by southerly transport and nearby northwestern regions.

Non-refractory PM2.5,Chemical species,Organic aerosol sources,Tianjin,Beijing,Warm seasons