Abstract. To better understand the origins, atmospheric processes and seasonality of atmospheric aerosols in North China, we collected fine aerosols (PM2.5) at an urban (Nankai District, ND) and a suburban (Haihe Education Park, HEP) sites in Tianjin from July 2018 to July 2019. The PM2.5 studied for carbonaceous, nitrogenous and ionic components and stable carbon and nitrogen isotope ratios of total carbon (δ13CTC) and nitrogen (δ15NTN). On average, mass concentration of PM2.5, organic carbon

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... OC), elemental carbon (EC) and water-soluble OC (WSOC found to be higher in winter than that in summer at both ND and HEP. SO42−, NO3− and NH4+ were dominant ions and accounted for 89 % and 87 % of the total ionic mass at ND and HEP respectively. NO3− and NH4+ peaked in winter and minimized in summer, whereas SO42− was higher in summer at both the sites. δ13CTC and δ15NTN were −26.5−(−)21.9 ‰ and +1.01−(+)22.8 ‰, respectively, at ND and −25.5−(−)22.8 ‰ and +4.91−(+)18.6 ‰, respectively, at HEP. Based on seasonal variations in the measured parameters, we found that coal and biomass combustion emissions are dominant sources of PM2.5 in autumn and winter, while biological and/or marine emissions are important in spring and summer in the Tianjin region, North China. In addition, our results implied that the secondary formation pathways of secondary organic aerosols in autumn/winter were different from that in spring/summer, i.e., they were mainly driven by NO3 radicals in the former period.