Black Carbon and Its Environmental Implications in the High Asia Atmosphere, Snow Cover, Lake, and Glaciers

Abstract:

High Asia (HA), extensively including Tibetan Plateau, Pamir, Tienshan, and Altai, is a wide region characterized by high mean elevation over 4000 m. It is thought to be a remote area with less pollution, although surrounded by populous regions of strong pollutant-emission, like South Asia and China. However, evidences from in-situ air monitoring data, ice core records, snow sample analysis, and lake sediment record showed that the environment of HA is more and more severely under the threat of pollutant locally generated and exotic. A three-year-round aerosol sampling in Pamir during 2003-2006 showed the concentrations of black carbon seemed to increase by a factor of 2. Trajectory analysis suggested the pollutants from the eastern parts of China should contribute large to this. Inside Tibet, the atmospheric BC at Nam Co also showed a slight increasing trend during 2006-2009 associated with the pollutant penetration from South Asia. Ice core records along the Himalaya showed black carbon from South Asia can be transported into Tibet primarily through the Brahmaputra river valley, and secondly by the uplifted air stream. The deposition of black carbon in the surface of HA glaciers can cause a mean forcing of 6 W/m2. The darkening of the mid-Himalaya glaciers can be partly due to black carbon. The mean concentration of BC in HA glaciers is ~50 ppbw, and that in the snow cover of Xinjiang is ~70 ppbw. BC can be responsible for 30% reduction in the albedo of a winter snow cover observed at Nam Co. A 150-year record retrieved from the sediment of Nam Co Lake showed a significantly increasing trend of BC since 1860, which is consistent with the emissions of South Asia. We conclude that BC from exotic surroundings has impacted the environment of HA significantly.