Distribution Characteristics and Health Risk Assessment of Heavy Metal Pollutants on Air Particulate Matters in Lanzhou City

In order to learn the present situation of heavy metals on particulate matters and evaluate their health risk, this paper cites the examples of District Xigu which is severely polluted and Town Yuzhong which is slightly polluted in Lanzhou city, the concentration of heavy metals attached on particulate matters in different seasons and different regions is measured, and the distribution proportion of heavy metals in different diameters of particulates is analyzed. Based on the health risk evaluation model recommended by USEPA, this paper evaluates health risks of pollution caused by heavy metals on atmosphere particulates at different sampling places in Lanzhou city. The result shows that heavy metal attached on particulate matter in Lanzhou city is distributed seasonally and regionally. Heavy metals on particulate matters in Lanzhou city are mainly attached on particulates of which the diameters are less than 10 mu m(PM10). In terms of horizontal gradient, the hazard index of heavy metal in the total suspension particulates in severely-polluted district of Lanzhou city in winter is greater than 1. In terms of vertical gradient, the hazard index of heavy metals on total suspension particulates 15m above ground in winter is greater than 1. These polluted aspects should be treated. The carcinogenic risk of chromium exceeds 10(-6)similar to 10(-4) which is acceptable scope stipulated by USEPA and should be well handled.