Combined influences of sources and atmospheric bleaching on light absorption of water-soluble brown carbon aerosols

Abstract Light-absorbing Brown Carbon (BrC) aerosols partially offset the overall climate-cooling of aerosols. However, the evolution of BrC light-absorption during atmospheric transport is poorly constrained. Here, we utilize optical properties, ageing-diagnostic δ 13 C-BrC and transport time to deduce that the mass absorption cross-section (MAC WS-BrC ) is decreasing by ~50% during long-range oversea transport, resulting in a first-order bleaching rate of 0.24 day ‒1 during the 3-day transit from continental East Asia to a south-east Yellow Sea receptor. A modern 14 C signal points to a strong inverse correlation between BrC light-absorption and age of the source material. Combining this with results for South Asia reveals a striking agreement between these two major-emission regions of rapid photobleaching of BrC with a higher intrinsic absorptivity for BrC stemming from biomass burni…