[A-AS11] Atmospheric Chemistry

[AAS11-P06] Both emissions and ageing altered brown carbon aerosols in the East Asian outflow

*Chunmao Zhu¹, Takuma Miyakawa¹, Fumikazu Taketani¹, Bhagawati Kunwar², Dhananjay Deshmukh², Kimitaka Kawamura², Yugo Kanaya¹ (1.JAMSTEC Japan Agency for Marine-Earth Science and Technology, 2.Chubu University)

Keywords:Brown carbon, Light-absorption properties, Photobleaching, Molecular tracers

Brown carbon (BrC), the light-absorbing fraction of organic aerosols, exerts significant influence on atmospheric radiative forcing, yet its source-specific optical properties and transformation processes remain poorly constrained. This study investigates the seasonal variability, source contributions, and atmospheric aging of BrC in the East Asian outflow, based on comprehensive observations at Fukue Island from November 2019 to November 2020. For the first time, we provide benchmark optical properties of BrC for climate models, demonstrating that the absorption coefficient and mass absorption cross-section of BrC from land-affected air masses are approximately twice those of sea-affected air masses. These distinct optical characteristics underscore the influence of source-region emissions on BrC’s radiative effects. We also quantify BrC photobleaching rates during long-range transport, revealing a half-life of ~1.9 days. Molecular tracer and isotopic analyses further indicate that fossil fuel combustion dominates BrC emissions in winter, while biomass burning peaks in spring, and biogenic sources contribute significantly in summer. Our findings highlight the importance of incorporating source-dependent BrC absorption properties and aging processes into climate models, improving predictions of BrC’s role in regional and global radiative forcing.