Spring-time enhancement in aerosol burden over a high-altitude location in western trans-Himalaya: results from long-term observations

Long-term measurements (from August 2009 to December 2014) of aerosol black carbon mass concentration (MBC) and spectral aerosol optical depth (AOD) were carried out from a high-altitude location, Hanle in western trans-Himalaya as part of the Regional Aerosol Warming Experiment. Both MBC and AOD showed distinct annual pattern with a clear spring-time enhancement (April-June) with significant inter-annual variability associated with the changes in source processes. The potential source regions contributing to the spring-time enhancement in aerosol loading are the dust-dominated west Asian region as well as biomass burning from NW India. The overall annual mean value of MBC over Hanle is extremely low compared to many other Himalayan locations, including the Ganges Valley Aerosol Experiment campaign site at Nainital, which also showed spring-time (pre-monsoon) enhancement. The vertical extents of elevated aerosol layers, which contribute to the spring-time enhancement, are found to be in the range 5-7 km amsl from the analysis of vertical profiles of extinction coefficients from CALIPSO data