Brown carbon aerosols in the Asian outflow region: Seasonal variations and source-specific light absorption properties

Light-absorbing organic aerosols (BrC) play a significant role in Earth's climate, but their sources and optical properties remain unclear. We investigated seasonal variations and source-specific contributions to BrC in the Asian outflow region, focusing on Fukue Island, a gateway from the continent to the North Pacific. We conducted parallel analyses of BrC light absorption and organic aerosol composition over a year. We found that BrC levels were markedly higher during winter-spring, coinciding with air masses carrying emissions from Asian sources. Water-soluble BrC absorption exhibited a strong correlation with a specific marker for fossil fuel combustion, suggesting its significant influence on BrC levels. Biomass burning emissions, as indicated by another marker, contributed to BrC levels, particularly in spring. The fraction of BrC soluble in methanol was significantly higher during summer, suggesting potential contributions from additional sources, such as local biogenic emissions, present in air masses from this period. This study sheds light on the seasonal dynamics and source-specific light absorption characteristics of BrC in the Asian outflow region. Our findings contribute to a better understanding of BrC sources and their impact on climate.