资源环境科技发展态势分析平台

Organic aerosols (OA) account for a large fraction of tropospheric fine particulate matter, but the hygroscopicity of OA is poorly understood. Here we show remarkably‐enhanced water uptake capacity of OA due to formation of highly‐oxidized oxygenated OA on new particle formation (NPF) events in Beijing. While non‐nucleation processes also produce oxidized OA, their hygroscopicity exhibits little enhancement. As a result, a correlation between the hygroscopicity and oxidation state is absent for OA on non‐NPF days. Further analysis reveals that the highly‐oxidized oxygenated OA is 2.5 and 5‐fold as hygroscopic as the oxidized primary OA and less‐oxidized oxygenated OA respectively. Our results suggest that nucleation‐initiated photooxidation of volatile organic compounds (VOCs) to produce water‐soluble organic acids may dominate on NPF days, and the aqueous oligomerization to yield less water‐soluble products might occur on non‐NPF days.