Water-Soluble Brown Carbon in Atmospheric Aerosols from Godavari (Nepal), a Regional Representative of South Asia

Brown carbon (BrC) has recently emerged as an important light-absorbing aerosol. This study provides interannual and seasonal variations in light absorption properties, chemical composition, and sources of water-soluble BrC (WS-BrC) based on PM10 samples collected in Godavari, Nepal, from April 2012 to May 2014. The mass absorption efficiency of WS-BrC at 365 nm (MAE(365)) shows a clear seasonal variability, with the highest MAE(365) of 1.05 +/- 0.21 m(2) g(-1) in premonsoon season and the lowest in monsoon season (0.59 +/- 0.16 m(2) g(-1)). The higher MAE(365) values in nonmonsoon seasons are associated with fresh biomass burning emissions. This is further substantiated by a strong correlation (r = 0.79, P < 0.01) between Abs(365) (light absorption coefficient at 365 nm) and levoglucosan. We found, using fluorescence techniques, that humic-like and protein-like substances are the main chromophores in WS-BrC and responsible for 80.2 +/- 4.1% and 19.8 +/- 4.1% of the total fluorescence intensity, respectively. BrC contributes to 8.78 +/- 3.74% of total light absorption over the 300-700 nm wavelength range. Considering the dominant contribution of biomass burning to BrC over Godavari, this study suggests that reduction in biomass burning emission may be a practical method for climate change mitigation in South Asia.