Chemical and stable carbon isotopic compositions of PM_2.5 from two typical forests in China: Implication for sources

Abstract. To elucidate the origin and seasonality of atmospheric aerosols in forest areas, simultaneous PM_2.5 collection was carried out in two typical forest sites: Changbai Mountain (CB, 42.40N, 128.11E), North China and Xishuangbanna (BN, 22.25N, 100.89E), South China, at day and night during the summer and winter periods of 2023–2024. Carbonaceous and nitrogenous components, water-soluble inorganic ions (WSIIs) and stable carbon isotopic composition of total carbon (δ¹³C_TC) were measured in PM_2.5. Generally, the contents of carbonaceous and nitrogenous components were higher in winter than summer, with secondary organic carbon (SOC) and water-soluble organic carbon (WSOC) higher in daytime than in nighttime at CB and BN. The average concentrations of WSIIs in total samples were 5.36 μg m^-3 and 2.23 μg m^-3 at CB and BN. SO₄^2-, NO₃^- and NH₄⁺ were dominant at CB, while SO₄^2-, NH₄⁺ and Na⁺ were dominant at BN, which accounted for 86 % and 89 % in BN to the total ions.δ¹³C_TC ranged from −27.8 ‰ to −22.1 ‰ at CB, while −27.6 ‰ to −24.5 ‰ at BN. Based on the results obtained, we found that besides biogenic emissions, the emissions from biomass burning and terrestrial and/or marine organisms were major sources of aerosols at both sites. Further fossil fuel combustion contributed more significantly at CB than at BN. Thus, this study provides insight into the origins and aging processes of PM_2.5 in forest areas in North and South China.