Aerosol black carbon over Bay of Bengal observed from an island location, Port Blair: temporal features and long-range transport

Abstract

Extensive measurements of the mass concentration of aerosol black carbon (BC) made for about 18 months during 2002–2003 from an island location, Port Blair, in the Bay of Bengal are used to characterize its temporal variations, mass mixing ratio, and association to air mass types. Significantly high concentrations (∼2.4 μg m⁻³) occur during prevalence of continental air mass, when it also depicts a high mass-mixing ratio (∼6.5%) to the composite aerosols. Diurnal variations show a nighttime peak and afternoon low, similar to those seen over the mainland, but weaker. Over the years, the concentrations are high during the September to April period, decrease rapidly (by a factor of >3) and continue to do so during the summer monsoon months (June to August). Back trajectory analyses reveal five potential advection pathways, which are seasonal in nature and have a strong influence on the BC concentrations over the island. Concentrations increase significantly, irrespective of air mass types, when the trajectories have long tracks close to and over land areas. The possible implications of the findings on radiative forcing are discussed.