Influence of Secondary Brown Carbon Aerosol Lifetime on Radiative Properties
Kang Hu, Hong Liao, Dantong Liu, Siyuan Li, Yangzhou Wu, Ping Tian, Fei Wang, Yuying Wang, Quan Liu, Zirui Liu, Bo Hu, Xiaotong Jiang, Shitong Zhao, Kai Bi, Delong ZhaoAbstract
Brown carbon (BrC), a light‐absorbing organic aerosol, exhibits higher absorption coefficients at short wavelengths. Partial BrC can be formed via secondary process. In this study, we isolated the secondary BrC ( σ abs,sec BrC ) between urban surface and mountain stations (which receive surface pollutants during convective mixing) to investigate how atmospheric lifetime variations influence its absorption properties. Although the surface provided more favorable conditions for precursor concentrations and physicochemical reactions, the surface station observed lower σ abs,sec BrC during the most developed planetary boundary layer period. This was driven by low temperatures and relative humidity (RH) during uplift, which extended the atmospheric lifetime of high‐viscosity secondary BrC, thereby enhancing σ abs,sec BrC observed at the mountain station. Variations in near‐surface emission intensity dominated peak σ abs,sec BrC values observed at the mountain station during 14:00–15:00. Moreover, decreasing RH promoted higher viscosity, which enhanced σ abs,sec BrC .