Leaves of Bauhinia blakeana as indicators of atmospheric pollution in Hong Kong

Bauhinia blakeana was used as a biomonitor to monitor the air quality in Hong Kong. Equations were set up to relate the ambient iron, copper, zinc and lead concentrations with those in leaves of the biomonitor and good correlations were observed. The concentration of sulphate in the leaves of Bauhinia blakeana was found to be directly related to ambient sulphur dioxide and total suspended particulates. Using these equations the ambient pollutant levels in different districts of Hong Kong were determined quantitatively according to the concentrations of pollutants in leaves. As many residential buildings are close to congested roads, the ambient pollutant concentrations at selected roads were evaluated. Many temples are known to be heavily polluted with air particulates, and thus the air quality inside are suspected to be poor. The air quality inside temples may be reflected by the air quality outside these buildings, which were also assessed using the proposed method of biomonitoring. The levels of ambient lead and copper outside these temples were higher than their respective background levels while the levels of pollutants at the kerbsides were reported to be 10–300% higher than those of the background.