Spatio-temporal characteristics of gaseous and particulate pollutants in an urban region of Kolkata, India

Abstract

This study deals with air quality monitoring in an urban region of Kolkata, consisting of residential, commercial and industrial sites having high population density and pollution. Concentrations of ambient SO 2 (sulfur dioxide), NO 2, (nitrogen dioxide), NH 3 (ammonia) and PM 10 (particulate matter passing through a size selective impactor inlet with a 50% efficiency cut-off at 10 μm aerodynamic diameter) were measured once in a week for 24 h at selected residential and industrial sites and 8 h at a commercial site. The meteorological parameters (wind speed, wind direction, rainfall, temperature and relative humidity) were collected simultaneously from the Indian Meteorological Department, Kolkata. The daily average concentrations of SO 2, NO 2, NH 3 and PM 10 were observed to be 12.3 ± 9.2, 32.5 ± 14.2, 36.3 ± 19.7 and 140.1 ± 43.1 μg/m 3 at the residential site, with 21.3 ± 15.7, 49.9 ± 9.8, 34.7 ± 13.5 and 196.6 ± 88.2 μg/m 3 at the industrial site, respectively. The corresponding (8 h average) values at the commercial site were 15.5 ± 11.9, 39.9 ± 17.3, 33.9 ± 13.3 and 276.1 ± 71.4 μg/m 3. Winter concentrations of ambient SO 2, NO 2, NH 3 and PM 10 were observed to be higher irrespective of the monitoring sites and duration of sampling, suggesting longer residence times of these pollutants in the atmosphere during winter due to stagnant conditions and low mixing heights. The SO 2/NO 2 ratios at the residential, commercial and industrial sites were found to be 0.38, 0.42 and 0.43, respectively. These low SO 2/NO 2 ratios are indicative of major emissions from mobile sources within the city. Spearman's rank correlation analysis showed an inverse relationship between the measured gaseous and particulate pollutant concentrations with the observed wind speed, rainfall, temperature and relative humidity. The data were analyzed using varimax-rotated principal component analysis for the residential and industrial sites. In principal component analysis three factors were drawn out of the seven variables, which represent 84% of the variance. The results show that local emissions dominate the concentration of SO 2, NO 2, NH 3, and PM 10. The major sources of emissions affecting this urban area include mobile sources along with contributions from industrial sources, coal-fired power plants and domestic heating.