Black carbon in cloud-water and rain water during monsoon season at a high altitude station in India

We present results of measurements of black carbon (BC) from ground-based wet-only rainwater (RW) and cloud-water (CW) sampling at a mountain field station, Sinhagad, situated in south western India during the period from June 2008 to October 2010. The amount of BC in the sample was determined by photometry at a wavelength of 528 nm after a procedure including the filtration through a 0.4 μm polycarbonate membrane filter. Water soluble concentrations of major anions in RW and CW were also determined. The average concentration of BC in RW (16 μmol dm−3) is higher by at least a factor 2 than that found in similar studies reported from other parts of the world. On the other hand, the average concentration of BC in CW (47 μmol dm−3) is lower by about a factor of 2 than that found at other sites. The ratio between the average concentrations in CW and RW varies from 2 (K+) to 7 (SO42−). The ratio for BC was about 3. No significant difference was observed for pH. Analysis of air mass back trajectories and of correlations between the various components indicates that long range transport of pollutants and dust from East Africa and Southern part of the Arabian peninsula might contribute to the high concentrations of BC and some of the ionic constituents at Sinhagad during the monsoon season.