Air quality is a major environmental problem in many developed and developing countries. Atmospheric pollution is mainly caused by high concentration of particulate matter (PM10, PM2.5), Oxides of Sulphur (SOx) and Oxides of Nitrogen (NOx) .If their concentration is more than tolerance limit of plants, they adversely affect plants. Variation of plants biochemical parameters like Relative water content (RWC), pH, Ascorbic acid and Total chlorophyll (TCh) content were found to be dependant on air quality. Air Pollution Tolerance Index of fifteen common tree species of Virudhunagar has been evaluated by analyzing these biochemical parameters. And percentage variation of these biochemical parameters with the control (Site 1) and polluted sites were established. Delonix regia and Moringa olifera showed higher percentage variation of ascorbic acid content variation (>100%) at heavy traffic area(Site 2) and species like Eugenia jambolana, Ficus religiosa, Ficus benghalensis, Eucalyptus globulus, Ficus benjamina showed higher percentage variation (>100%) at industrial area (Site 3). Tree species like Delonix regia, Moringa olifera showed higher % variation of TCh at site 2(>100%). And species like Moringa olifera and Ficus benghalensis exhibited higher variation of TCh at site3 (>100%). Leaf pH did not show considerable variation. Eugenia jambolana showed 20% variation at Site2. Tamarindus indica, Mangifera indica, Eugenia jambolana and Tectona grandis showed 21%, 27%, 23%, 37% variations at site 3..Higher variation of RWC was observed in Ficus bengamina at site 2 (79%) and Polyalthia longifolia at site3 (33%) .Thus out of fifteen species of plants studied only 4 species served as indicator of air pollution namely Ficus benghalensis,Tectona grandis,Eucalyptus globulus and ,Ficus benjamina.Eventhough Delonix regia is a sensitive species it becomes tolerant in industrial area.
