Within certain limits of concentration, woody-plants not only can resist, in some degree, pollutants, but also have certain ability to absorb them. Therefore, the leaves of trees can used for absorbing and cleaning air pollutants, and as indicators of air pollution.Leaves of some kinds of woody-plants play an important part in absorbing and accumulating the gaseous pollutants, such as SO2, Cl2, HF and so on. The abilities of absorption are variable accoroding to different tree-species. The correlation betwe...