Influence of anthropogenic emissions on wet deposition of pollutants and rainwater acidity in Guwahati, a UNESCO heritage city in Northeast India

摘要

Guwahati, the largest urban corridor of Northeast India, is one of the United Nations Educational, Scientific and Cultural Organization (UNESCO) world heritage sites and one of the 200 eco-regions in the world. The present study investigates the characterization of chemical components and sources of precipitation samples collected in Guwahati during June 2016-June 2017. Acidic rain events occurred throughout the year, with a frequency of 64% and 87% during monsoon and non-monsoon seasons, respectively. Higher contributions of the acidic species (SO42- and NO3-) coinciding with poor neutralizing capacity of crustal species (Ca2+, K+ and Mg2+) led to acid rain in this region. Isotope analysis (delta O-18 and delta D) indicated that monsoonal and non-monsoonal rains were of marine and non-marine origins, respectively. This is further supported by the back trajectory analysis as majority of the individual rain events during d-excess < 10% i.e. monsoon, indicated their maximum contribution from ocean while, during d-excess> 10% i.e. non-monsoon, the trajectories originated from water-inland. The enrichment factors (EF) for Pb, Zn, Co and Cu were > 5, indicating the dominance of anthropogenic sources in this region. The Positive Matrix Factorization (PMF) along with isotope analysis identified marine (40%) as the major source in monsoon and industrial emissions (28%) in non-monsoon, indicating rainwater evaporation is more of ocean and continental origin during monsoon and non-monsoons, respectively. This study suggests the need of further studies and implementation of stringent anthropogenic regulations not only in local but also at regional and global scale, in this acid rain prone region.