. Removal of Air Pollutants: Trees can remove gaseous air pollution either through uptake via leaf stomata or the plant surface. Once inside the leaf, gases diffuse into intercellular spaces and may be absorbed by water films to form acids or react with inner-leaf surfaces. Recent research suggests that the planting of trees along the sides of roads could reduce NO2 concentrations in addition to providing amenity value [1]. Trees can also remove pollution by intercepting airborne particles. Some particles can be absorbed into the tree, though most that are intercepted are retained on the plant surface. The intercepted particle is often re-suspended to the atmosphere, washed off by rain, or dispersed through leaf fall. Consequently, vegetation is thought to be only a temporary retention site for many atmospheric particles.