Impacts of biomass burning and photochemical processing on the light absorption of brown carbon in the southeastern Tibetan Plateau

[摘要] Brown carbon (BrC) in the atmosphere can greatlyinfluence aerosol's radiative forcing over the Tibetan Plateau (TP) becauseit has the non-negligible capacity of light absorption compared to blackcarbon (BC); however, our understanding of optical properties, sources,and atmospheric processes of BrC in this region remains limited. In this study,a multiple-wavelength Aethalometer coupled with a quadrupole aerosolchemical speciation monitor was deployed to investigate the highly timeresolved BrC in the submicron aerosol at the southeastern edge of the TPduring the pre-monsoon season. The results showed that BrC madesubstantial contributions (20.0 %–40.2 %) to the light absorption ofsubmicron aerosol from 370 to 660 nm. Organic aerosol (OA), an alternativeto BrC, was split into a biomass burning OA (BBOA) with aging processes and aphotochemical-oxidation-processed oxygenated OA (po-OOA) by a hybridenvironmental receptor model analysis. Combined with the light absorptioncoefficient of BrC ( b abs-BrC ), the source-specific mass absorption crosssections of BBOA (0.61–2.78 m 2  g −1 ) and po-OOA (0.30–1.43 m 2  g −1 ) at 370–660 nm were retrieved. On average, b abs-BrC from po-OOA (1.3–6.0 Mm −1 ) was comparable to that fromBBOA (1.3–6.0 Mm −1 ) at all wavelengths. The concentration-weightedtrajectory analysis showed that the most important potential source regionsfor b abs-BrC values from BBOA and po-OOA were located in northernMyanmar and along the China–Myanmar border, indicating the cross-bordertransport of BrC from Southeast Asia. A “simple forcing efficiency”evaluation further illustrated the importance of the BrC radiative effect withthe high fractional radiative forcing by two OAs relative to BC (48.8  ±  15.5 %). This study highlights a significant influence of BrC ofbiomass burning origin and secondary formation on climate change over the TPregion during the pre-monsoon season.

[学科分类] 医学（综合）