Strong radiative heating due to wintertime black carbon aerosols in the Brahmaputra River Valley

摘要

The Brahmaputra River Valley (BRV) of Southeast Asia recently has been experiencing extreme regional climate change. A week-long study using a micro-Aethalometer was conducted during January-February 2011 to measure black carbon (BC) aerosol mass concentrations in Guwahati (India), the largest city in the BRV region. Daily median values of BC mass concentration were 9-41 gm ~(-3), with maxima over 50 gm ~(-3) during evenings and early mornings. Median BC concentrations were higher than in mega cities of India and China, and significantly higher than in urban locations of Europe and USA. The corresponding mean cloud-free aerosol radiative forcing is -63.4 Wm ~(-2) at the surface and +11.1 Wm ~(-2) at the top of the atmosphere with the difference giving the net atmospheric BC solar absorption, which translates to a lower atmospheric heating rate of ～2K/d. Potential regional climatic impacts associated with large surface cooling and high lower-atmospheric heating are discussed.