Benzene is a naturally occurring colourless liquid at room temperature (25 ^oC) and pressure (760 mm Hg).  It has a characteristic aromatic odour, a relatively low boiling point (80.1^oC) and high vapour pressure, which causes it to evaporate rapidly at room temperature.  Benzene is released into the environment from both natural and man-made sources, although the later is the most significant source.  Benzene in air exists predominantly in the vapour phase, with residence time varying between few hours to a few days depending on the environment and climate. Degradation of benzene in air occurs mainly by reaction with hydroxyl, alkoxy and peroxy radicals. Toluene and Xylene are also present in most of the sources along with Benzene.  Physico-chemical properties of Benzene, Toluene & Xylene are given in Table : 1.