Measurement Report: Chemical components and ¹³C and ¹⁵N isotope ratios of fine aerosols over Tianjin, North China: Year-round observations

Abstract. To better understand the origins, atmospheric processes and seasonality of atmospheric aerosols in North China, we collected fine aerosols (PM_2.5) at an urban (Nankai District, ND) and a suburban (Haihe Education Park, HEP) sites in Tianjin from July 2018 to July 2019. The PM_2.5 studied for carbonaceous, nitrogenous and ionic components and stable carbon and nitrogen isotope ratios of total carbon (δ¹³C_TC) and nitrogen (δ¹⁵N_TN). On average, mass concentration of PM_2.5, organic carbon (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. δ¹³C_TC and δ¹⁵N_TN 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 PM_2.5 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.