Anthropogenic emissions of black carbon (BC) aerosol are transported from Southeast Asia to the southwestern Tibetan Plateau (TP) during the pre-monsoon; however, the quantities of BC from different anthropogenic sources and the transport mechanisms are still not well constrained because there have been no high-time-resolution BC source apportionments. Intensive measurements were taken in a transport channel for pollutants from Southeast Asia to the southeastern margin of the TP during the pre-monsoon to investigate the influences of fossil fuels and biomass burning on BC. A receptor model that coupled multi-wavelength absorption with aerosol species concentrations was used to retrieve site-specific Ãngström exponents (AAEs) and mass absorption cross sections (MACs) for BC. An "aethalometer model" that used those values showed that biomass burning had a larger contribution to BC mass than fossil fuels (BC.sub.biomass =57 % versus BC.sub.fossil =43 %). The potential source contribution function indicated that BC.sub.biomass was transported to the site from northeastern India and northern Burma. The Weather Research and Forecasting model coupled with chemistry (WRF-Chem) indicated that 40 % of BC.sub.biomass originated from Southeast Asia, while the high BC.sub.fossil was transported from the southwest of the sampling site. A radiative transfer model indicated that the average atmospheric direct radiative effect (DRE) of BC was +4.6 Â± 2.4 W m.sup.-2, with +2.5 Â± 1.8 W m.sup.-2 from BC.sub.biomass and +2.1 Â± 0.9 W m.sup.-2 from BC.sub.fossil . The DRE of BC.sub.biomass and BC.sub.fossil produced heating rates of 0.07 Â± 0.05 and 0.06 Â± 0.02 K d.sup.-1, respectively. This study provides insights into sources of BC over a transport channel to the southeastern TP and the influence of the cross-border transportation of biomass-burning emissions from Southeast Asia during the pre-monsoon.