Source Apportionment Of PM_2.5 And Risk Assessment Of Heavy Metals In A Coal Based City

With the rapid development of China’s economy and society,the poor air quality remains lots of concerns from the government and public,especially in some small and medium-sized coal based cities.The forming factor of haze is the pollution of fine particulate matter(PM_2.5).In order to reduce the concentration of PM and improve the air quality,source apportionment and source contribution of PM_2.5 are significant for the whole study.Coal resource-based city Changzhi was selected as the research object.145 samples were collected during 2017/10/14-2017/12/5 and analyzed by PMF model,Back-ward trajectory analysis and PSCF.The EFs and the Igeo methods were used to judge the degree of pollution and enrichment of elements.The risk assessment of contaminated heavy metals was carried out by the human health exposure risk model.The conclusions obtained are as follows:The average concentration of PM_2.5 in City Changzhi was 67.2±30.4μg·m^-3,of which about 22.5%exceeds the national air quality secondary standard limit,and about89.8%exceeds the US EPA air quality standard limit.The average concentration of water-soluble ions was 5.99±5.06μg·m^-3,accounting for 9.66%of PM_2.5 concentrations.The main water-soluble cations were NH₄⁺（21.88%）and Ca²⁺（6.32%）.The main water-soluble anions were NO₃^-（34.14%）,SO₄^2-（24.04%）and Cl^-（8.78%）.The ratio of AE/CE was 0.87 which represented the atmospheric aerosol was alkaline.The results of source apportionment by PMF model showed six main pollution sources.They were secondary aerosols（29.93%）,coal combustion（24.76%）,biomass burning（16.72%）,dust（12.48%）,industrial emissions（9.13%）and vehicle emissions（6.97%）。There were three types of air mass by simulation of back-ward trajectory.The first contributed 56.96%from Mongolia,Inner Mongolia,Gansu,Ningxia,Shaanxi.The trajectory 3 with 25.49%contribution carried the highest PM_2.5 concentration(117.88μg·m^-3).The results of PSCF indicated that the main source of pollutants in City Changzhi was local contribution.The results of EFs and Igeo methods showed the seriously affected elements were Zn,As,Cd,Sn,Sb,Tl and Pb.V,Cr and Cu were contaminated by both artificial and natural sources.The results of human health risk assessment for the ten elements with high enrichment and serious pollution indicated that As and Cr posed a carcinogenic risk to residents of City Changzhi through different routes.It’s also worth noting that the combined effect of ten elements had a non-carcinogenic risk value of 1.1 for children by ingestion,which was harmful to their health.