Reply on RC1

Abstract

Brown carbon (BrC) in the atmosphere can greatly influence aerosol’s radiative forcing over the Tibetan Plateau (TP), because it has the non-negligible capacity of light absorption as well as black carbon (BC); however, our understanding of optical properties, sources, atmospheric processes of BrC in this region remains limited. In this study, a multiple-wavelength Aethalometer coupled with a quadrupole aerosol chemical speciation monitor were deployed to investigate the highly time resolved BrC in the submicron aerosol in the southeastern edge of the TP during the pre-monsoon season. The result showed that BrC had the substantial contributions (20.0–40.2 %) to the light absorption of submicron aerosol from 370 to 660 nm. Organic aerosol (OA), an alternative to BrC, was split into a biomass burning OA (BBOA) with aging process and a photochemical-oxidation processed oxygenated OA (po-OOA) by a hybrid environmental receptor model analysis. Combined with light absorption coefficient of BrC (babs-BrC), the source-specific mass absorption cross section of BBOA (0.50−1.75 m2 g-1) and po-OOA (0.38−2.15 m2 g-1) at 370−660 nm were retrieved. On average, babs-BrC from po-OOA (1.1−6.3 Mm-1) was higher than that from BBOA (0.7−2.3 Mm-1) at all wavelengths. The concentration weighted trajectory analysis showed that the most important potential source regions for babs-BrC values from BBOA and po-OOA were located in the northern Myanmar and along the China-Myanmar border, indicating the cross-border transport of BrC from Southeast Asia. A "simple forcing efficiency" evaluation further illustrated the importance of BrC radiative effect with the high fractional radiative forcing by two OAs relative to BC (50.6 ± 18.7 %). This study highlighted a significant influence of BrC from biomass burning emissions and secondary formation on climate change over the TP region during the pre-monsoon season.