Evaluation of ambient air quality in Dehradun city during 2011-2014

The variations in the ambient concentrations of particulate matter (SPM and PM10) and gaseous pollutants (SO2 and NO2) at Clock tower (CT), Rajpur road (RR) and Inter State Bus Terminal (ISBT) station in Dehradun city, Uttarakhand, India are analysed for the period of 2011-2014.Mean concentrations are observed to be higher during pre-monsoon season as compared to the winter and monsoon. PM10 and SPM concentrations with maximum values of 203 +/- 23 and 429 +/- 49m-3, respectively, during winter, are found to exceed the national standards by factors of 2 and 3. Winter-time elevated pollution in Dehradun is attributed to the lower ventilation coefficient (derived from Era interim model fields) and minimal precipitation. Nevertheless, the SO2 and NO2 levels are observed to be within the criteria notified by the Central Pollution Control Board (CPCB), India. Correlation analysis shows profound impacts of the meteorology and local dynamics on the observed variations in observed trace species. Additionally, the stronger inter-species correlation variations (r=0.79 for SO2 with NO2, and r=0.89 for PM10 with SPM), which may suggest their origin from common sources. Analysis of Air Quality Index (AQI)' variations indicates unhealthy atmospheric conditions near the major city centers and bus station. More observations in the region are highly desirable to understand the dispersion of the enhanced pollution in the Dehradun valley.