Abstract
The last decade in India has seen a rapid deterioration in the air quality in its major cities. This has led to increased interest from the general public to their exposure to ambient air quality primarily because of the effects of such air pollutants on human health. In this context, the air quality indices (AQI) is often used by the local authorities to signify the levels of the seriousness of air pollution to the common public. The use of air quality indexing for assessment of existing air quality standards has been widely used for different cities in India and the world. The paper presents the application of air quality indices for assessing the existing air quality standards in an Indian city, Shimla. The indices have been calculated using the methodology described by the US Environmental Protection Agency (USEPA), which is adopted by the Central Pollution Control Board (CPCB) in India. An alternative method for determination of air quality indices is also utilized (referred to as AQIam for the Indian context. The estimates air quality indices are applied to two monitoring sites (Tekka Bench, Ridge and ISBT bus stand) in Shimla city over the study period (2004-2015) on the pollutants: Sulphur dioxide (SO2), oxides of nitrogen (NOx), suspended particulate matter (SPM) and respirable suspended particulate matter (RSPM). The annual air quality indices results for the study period showed that the air quality was 'good' for Tekka Bench monitoring station for the entire study period and for the ISBT bus stand for all the years, except 2011 when it was in ‘moderate' category. The annual air quality indices predicted using the alternative methodology indicated the level of air quality to be 'good' for the entire study period, except 2013 when it was classified as ‘satisfactory' for the monitoring site at Tekka Bench. Similarly, the annual air quality was classified as 'moderate’ for the years 2011, 2013-2015 for the monitoring station at ISBT bus stand site with the remaining years of the study period being classified as 'good'. These categorizations of existing air quality interpret the expected health effects of exposure to surrounding ambient air. Higher the value of air quality indices more severe is the categorization and thereby more harmful are the human health effects being exposed to ambient air conditions. Similar such seasonal variations of air quality indices were also observed during the study period at both the monitoring sites.