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 PM2.5 collection was carried out in two typical forest sites: Changbai Mountain (CB, 42.40° N, 128.11° E), North China and Xishuangbanna (BN, 22.25° N, 100.89° E), South China, at day and night during the summer and winter periods of 2023–2024. Carbonaceous and nitrogenous components, water-soluble inorganic ions (WSII) and stable carbon isotopic composition of total carbon (δ13CTC) were measured in PM2.5. Generally, the contents of carbonaceous and nitrogenous components were higher in winter than in summer, with secondary organic carbon (SOC) and water-soluble organic carbon (WSOC) being higher in daytime than that in nighttime at both CB and BN. The average concentrations of WSII in total samples were 5.36 and 2.23 µg m−3 at CB and BN, respectively. SO42-, NO3- and NH4+ were dominant at CB, while SO42-, NH4+ and Na+ were dominant at BN, which accounted for 86 % and 89 % to the total ions, respectively. δ13CTC ranged from −27.8 ‰ to −22.1 ‰ at CB, while −27.6 ‰ to −24.5 ‰ at BN. Besides biogenic emissions, the emissions from biomass burning and terrestrial and/or marine organisms were major sources of aerosols at both sites. Furthermore, fossil fuel combustion contributed more significantly at CB than at BN in winter. This study sheds better light on the seasonality in chemical composition and origins of PM2.5 in forest areas in North and South China.