10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Evaluating Inter-seasonal Urban Environment-mixed Black Carbon-induced Radiative Effects over Eastern India
SHUBHA VERMA, Shantanu Pani, Sanhita Ghosh, Sauvik Santra, Indian Institute of Technology Kharagpur
Abstract Number: 1695 Working Group: Carbonaceous Aerosol
Abstract The abundance of absorbing aerosols during the pre-monsoon season, consisting of locally emitted black carbon (BC) and of dust transported from near-by and far-off region have been suggested leading to elevated atmospheric heating effect. Sensitivity experiments using state of the art aerosol-chemistry-climate models reveal impacts of prevalent absorbing aerosols during the pre-monsoon season on the monsoon precipitation over India. Since atmospheric BC concentrations peak close to major source regions thus giving rise to regional hot-spots, BC-induced radiative warming effect could be more significant on a local to regional scale than the global, which in turn can have strong implications for the regional hydrological cycle. It is difficult to quantify such effects at a finer resolution of the urban scale using large-scale chemistry-climate models due to their coarser resolution and inefficiency to simulate fine scale aerosol properties.
Long-term observations of BC aerosols encompassing all seasons in an urban atmosphere in eastern India provided a unique opportunity to quantify the inter-seasonal urban environment-mixed BC-induced radiative effects. Under an influence of inter-seasonal transport processes and season-specific anthropogenic activity, urban environment-mixed BC-induced radiative effects were evaluated in the vicinity of aerosol composition constituted of enhanced anthropogenic constituents during winter/northeast monsoon season and elevated dust storms during summer/southwest monsoon season. In the present study, we applied a receptor modelling approach to quantify these effects. This was done through the application of long-term simultaneous observations of BC in conjunction with the total aerosol concentration and aerosol optical properties in the configuration of aerosol optical and radiative transfer model. Modelling experiments were designed using this model to simulate urban environment-mixed BC-induced radiative effects.
Our study indicated while the surface BC concentration exhibited a large seasonal variability, the value of BC-AOD was consistently high throughout; except during southwest monsoon season when this value was lower by about three times than that during rest of the seasons. A considerable change in the net radiation balance and an enhancement in radiative forcing efficiency and the atmospheric heating rate was estimated when BC was mixed with atmospheric aerosol constituents compared to unmixed BC; seasonal mean radiative forcing efficiency values due to mixed BC was about 8 to 13 times the unmixed BC value at the top-of-atmosphere. The urban environment-mixed BC-induced radiative heating effect during summer was estimated being higher than during southwest monsoon by 13% only, compared to by a factor of two times during winter season. While the summertime mean value of radiative forcing efficiency was about two times, the southwest monsoon mean value of the same was five to seven times the value during winter at all layers of the atmosphere. Enhanced urban environment-mixed BC-induced net radiative warming effect inferred during summer and southwest monsoon season was found consistent with our postulate about the possible signatures of this estimated effect in real observations of seasonal surface temperature features. Our study thus suggests mitigation of BC emissions may not be sufficient to curb urban environment-mixed BC-induced warming effect under the prevalence of prominent dust transport; thus drawing attention towards the complex role of mitigation measures to reduce pollution-induced radiative effects and its impact on regional climate.