Black carbon aerosol in winter northeastern Qinghai-Tibetan Plateau, China: the effects from South Asia pollution.

Black carbon (BC) aerosol at high-altitude Qinghai-Tibetan Plateau has potential effects on the regional climate and hydrological cycle. An intensive measurement campaign was conducted at Qinghai Lake (~ 3200 a.s.l.) at the edge of the northeastern Qinghai-Tibetan Plateau during winter using a ground-based single particle soot photometer (SP2) and a photoacoustic extinctiometer (PAX). The average BC concentration and number fraction of coated BC were found to be 160±190 ng m^-3 and 59.3% for the entire campaign, respectively. Significant enhancements of BC loadings and number fraction of coated BC were observed during pollution episode, with an average value of 390 ng m^-3 and 64.6%, respectively. The mass size distribution of BC particles showed lognormal distribution with a peak diameter of ~ 187 nm regardless of the pollution level. Five-day backward trajectory analysis combined with the fire counts map suggests that the biomass burning air masses from North India contributing to the increased BC loadings during the campaign. The potential source contribution function (PSCF) model further proves that North India is an important potential region influencing northeastern Qinghai-Tibetan Plateau during the pollution episode. The BC mass absorption cross section (MAC_BC) at λ= 532 nm was slightly larger during pollution episode (10.2 m² g^-1) than in clean days (8.9 m² g g^-1), likely due to the higher mixing state of BC with other chemical components during pollution episode. The number fraction of coated BC particles showed positive correlation with light absorption, suggesting that the increase of coated BC particles will enhance the light absorption. The estimated BC direct radiative forcing was + 0.93W m² for pollution episode, which is 2 times larger than that in clean days. Our study provides insight into the potential climatic impacts of BC aerosol transported to the Qinghai-Tibetan Plateau from South Asian regions, and is also useful for future modeling studies. [ABSTRACT FROM AUTHOR]