Although water and land pollution are very dangerous, air pollution has its own peculiarities due to its transboundary dispersion of pollutants over the entire world. In any well planned urban set up, industrial pollution takes a back seat and vehicular emissions take precedence as the major cause of urban air pollution. In the present study, air pollution tolerance index was calculated for various plant species growing at two sites Nagal village at Sahastradhara Road and the Clock Tower (the experimental site) of Dehradun city, India. The leaf samples were collected from 7 commonly present tree species. The results showed significant effects of various air pollutants on the vegetation in terms of four biochemical parameters analysed. Four physiological and biochemical parameters, which are leaf relative water content, Ascorbic acid content, total leaf chlorophyll content and leaf extract pH were used to compute the air pollution tolerance index values. Statistically significant difference was observed between control and experimental group for Ascorbic acid, t(6)=-4.848,p=.003. Paired t test for air pollution tolerance index between the two groups showed a statistically significant difference, t (6)=-4.548, p=.004. On the basis of air pollution tolerance index values for above mentioned seven tree species, Eucalyptus globus exhibited the highest degree of tolerance at all the sites followed by Ficus religiosa >Mangifera indica > Polyalthia longifolia > Phyllanthus emblica > Citrus limon > Lantana camara.