Sources of Black Carbon Aerosols in South Asia and Surrounding Regions During the Integrated Campaign for Aerosols, Gases and Radiation Budget (ICARB)

The dominant sources of black carbon (BC) in South Asia and surrounding regions are inferred during March-May 2006 (Integrated Campaign for Aerosols, Gases and Radiation Budget (ICARB)) by introducing BC tracers in the Weather Research and Forecasting Model coupled with Chemistry. Model results show that ICARB measurements were fairly well representative of the Arabian Sea and the Bay of Bengal during the pre-monsoon season. The model reproduced well the magnitude, temporal and spatial variability of BC concentrations observed during the ICARB ship-cruise. Average and standard deviation (representing the spatial and temporal variability) in observed and modeled BC mass concentrations along the ship-track are estimated as 755±734 ng m^-3 and 732±913 ng m^-3 respectively, where the standard deviation represents the spatial and temporal variability in the region. Average modeled values at most of the inland stations were also found to fall within the range of observed values. Results show that anthropogenic and biomass burning emissions, respectively, accounted for 70% and 28% of the BC mass concentration in South Asia. BC emissions from residential (49%) and industrial (37%) sectors appear to be the major anthropogenic sources, except in the Himalayas where vehicular emissions dominate. We find that, while all parts of continental India contributed to anthropogenic BC over Bay of Bengal, contribution over the Arabian Sea came mostly from southern Peninsula. We also show that long-range transport of anthropogenic emissions contribute up to 30% of BC concentrations in western and eastern India, suggesting that it is important to consider non-local sources along with the local emissions while designing strategies for mitigating BC emissions.