Ambient Air Quality Analysis in Shimla City: a modelling approach

Abstract

This study evaluated the existing ambient air quality of Shimla city for period of 2011-2017. The monitoring is conducted at two locations which are representative of two different conditions within city representing two distinct monitoring classifications- an urban and a background site. The assessment was based on several parameters. Short term variations in air quality was analysed by studying the change in concentrations of air pollutants for the festival of Diwali and compared with normal day concentration of pollutants. The higher levels of degradation was noted at monitoring site II i.e. the urban site where combined effect of vehicular emissions and firework activities affected the concentration of pollutants. It was observed that pyrotechnic activities had significant influence on concentrations of air pollutants especially RSPM. The results of short term analysis was validated by determination of Air Quality Index. Long term trends were analysed by studying the annual and seasonal variations in concentrations of air pollutants. The degree of pollution at two monitoring sites was observed using Annual Exceedance factor. The annual mean concentrations of NO2 and SO2 were found to be well within NAAQS standards, however annual average concentrations of RSPM crossed the standards several times. It was also noticed in seasonal analysis that concentrations of only particulate matter significantly varied during the seasons. Highest concentrations were observed during the summer season, with lowest levels of particulates were noted in rainy season. A regression analysis for determining the association of monitored air pollutants with meteorological parameters was conducted. Modelling studies revealed the use of STREET and CALINE 4 models for prediction of ambient air quality of Shimla city. Further, another focal point of research is absence of adequate monitoring stations and techniques and hence inability to represent the existing air quality of the entire city.