Contributions of different organic compounds to brown carbon light absorption in a river-valley region, China

Brown carbon (BrC) is a unique category of organic carbon aerosol that absorbs ultraviolet–visible light, influencing the radiative budget and climate change. An intensive observational study was conducted in a representative river-valley city in China to investigate the contributions of various organic aerosols (OA) to BrC light absorption. The influence of each OA component on BrC absorption exhibited fluctuations across different air quality levels and diurnal cycles, reflecting changes in emissions and meteorological conditions. Our results demonstrate that biomass-burning OA (BBOA) accounted for 33% of the BrC absorption at a wavelength of 370 nm, surpassing the contributions of coal combustion OA (CCOA) at 30% and cooking OA (COA) at 29% during the observation period. Notably, BBOA's contribution to BrC absorption intensified as air quality deteriorated from excellent to polluted, whereas COA's contribution decreased. The impact of CCOA on BrC absorption showed minor variations with air quality. Additionally, the source contributions to BrC absorption differed between daytime and nighttime, with CCOA dominating during daytime and BBOA leading at night. This study enhances our comprehension of BrC's optical characteristics and the array of sources influencing its light absorption in river-valley regions.