Seasonal variation in the spatial distribution of aerosol black carbon over Bay of Bengal: a synthesis of multi-campaign measurements

Abstract

Synthesizing data from several cruise experiments over the Bay of Bengal (BoB), the seasonal characterization of aerosol black carbon (BC) mass concentration was made. The study indicated that the BC mass concentration (M_BC) showed significant seasonal variation over the oceanic region with M_BC being the highest during the winter season (∼2407 ± 1756 ng m⁻³) and lowest in summer monsoon (∼765 ± 235 ng m⁻³). The seasonal changes in the BC mass concentration were more prominent over the northern BoB (having an annual amplitude of ∼4) compared to southern BoB (amplitude ∼ 2). Significant spatial gradients in M_BC, latitudinal as well as longitudinal, existed in all the seasons. Latitudinal gradients, despite being consistently increasing northwards, were found to be sharper during winter and weakest during summer monsoon with e-fold scaling distances of ∼7.7° and ∼15.6° during winter and summer monsoon seasons respectively. Longitudinally, BC concentrations tend to increase toward east during winter and premonsoon seasons, but an opposite trend was seen in monsoon season highlighting the seasonally changing source impacts on BC loading over BoB. Examination of the results in light of possible role of transport from adjoining landmasses, using airmass back trajectory cluster analysis, also supported spatially and temporally varying source influence on oceanic region.