Long range transport and wet deposition fluxes of major chemical species in snow at Gulmarg in North Western Himalayas (India)

Abstract

The study reports snow chemistry and long range transport of pollutants at Gulmarg in north-western Himalayan region of India during winters of 2012-2013. The pH of snowmelt varied between 5.16 and 7.68 with an average of 5.90. The frequency distribution of pH of snowmelt showed that the maximum number of samples (31%) had pH between 6.81 and 7.20. However, 12% samples were observed to be acidic (below 5.6). Scavenging ratios (SR) values suggested that crustal components (Ca2+, Mg2+) are efficiently removed by snow. The study site has significant influence of non-marine sources. Wet deposition contributed 34, 27, 45, 71, 8 and 13 meq m-2 fluxes of nssSO42-, NO3-, NH4+, nssCa2+, nssMg2+ and nssK+ respectively. Both local emissions as well as long range transport (LRT) of pollutants were found to be the sources of these ionic species. Backward airmass trajectory calculations showed that this site received airmasses from six major sectors i.e., i) North Atlantic Ocean origin (NAO), ii) African origin (Af), iii) Middle East origin (ME), iv) European origin (Eu), v) Western India origin (InW), vi) Pakistan origin (Pk). The highest average pH (7.58) of the snowfall was noticed during InW airmasses which had the lowest ratios of nssSO42-/nssCa2+ and NO3-/nssCa2+. Very high pH has been observed in precipitation samples at Indian sites due to buffering of acidic components by atmospheric dust rich in CaCO3. The lowest pH (4.94) was noticed for ME airmasses which had the highest nssSO42-/nssCa2+ and NO3-/nssCa2+ ratios. Data of present study was compared with a study reported almost three decades ago. We noticed a drastic increase in the concentrations of anthropogenic components such as nssSO42- (114%), NO3- (109%) and NH4+ (90%). This is probably due to increase in LRT of pollutants as well as local activities during past three decades.