Seasonal variation in the ambient air quality of a tropical city Varanasi, India - A case study

Seasonal variation in the concentration of sulphur dioxide (SO2), nitrogen dioxide (NO2) and suspended particulate matter (SPM) in the ambient air in a tropical city, Varanasi, India were studied during the period from June 2004 to May 2005. Ambient air samples were collected from four sampling sites and analyzed for some physico-chemical properties such as NO2, SO2 and SPM. The highest concentration of SO2 (91.4 mu g/m(3)) and NO2 (84.2 mu g/m(3)) during January were observed at Andharapul site, whereas lowest concentration of SO2 (12.8 mu g/m(3)) and NO2 (11.6 mu g/m(3)) were observed during July at the Banaras Hindu University Campus site. The maximum concentration of SPM (695 mu g/m(3)) was recorded at Andharapul during May and minimum (45 mu g/m(3)) during the July at Banaras Hindu University Campus. SO2 and NO2 showed decreasing trend from winter to rainy season months. However, SPM did not show similar trend. A negative and significant correlation was noted between ambient air temperature and SO2 as well as NO2 concentration, whereas positive correlation between SPM and ambient air temperature was observed. From general survey of sources of air pollutants on all the four study sites, the automobile emissions were found to be the major -source of air pollution. Present investigation revealed the level of pollution on different sites as Andharapul > Godowalia > Lahurabir. The BHU Campus site was found unpolluted throughout the investigation period.