Spatial-temporal Variation,Sources And Risk Assessment Of Heavy Metals In Ambient PM_2.5 Of Nanjing

Daily PM2.5 samples were collected around the 2016 at an urban and suburban site of Nanjing and analyzed for 12 kinds of heavy elements. Their concentrations and spatial-temporal variation were analyzed. Their sources were analyzed by enrichment factor, cluster analysis, principal component analysis (PCA) and positive matrix and factorization (PMF).The risks of heavy metals to human health were assessed. Results showed that:(1)During the sampling period,the average mass concentration of PM2.5 was 66.8 and 63.5 μg/m3 in the suburban and urban site.The mass concentrations of PM2.5 were in the order of winter(84.3±36.6 μg/m3)>autumn(53.9±17.7 μg/m3) >spring(42.1±15.8 μg/m3)>summer(42±9.3 μg/m3) in the urban site.They were in the order of winter(83.5±37.9 μg/m3) > autumn(61.3±31 μg/m3) > spring(49.8±13.8μg/m3)>summer(40.3±9.7 μg/m3)for the suburban site.(2)The concentration of the heavy metals were higher in the rural site than the urban sitel. During the sampling period, the main elements of the heavy metals were Zn, Cu, Pb, Mn, contributing by 44.4%, 26.8%, 14.6% and 5.9% in the suburban site, while contributing by 46.8%, 24.5%, 13.2% and 24.5% in the urban site,respectively.(3)Enrichment factor showed that Cd, Sb, Pb, Cu, and Zn were heavily enriched in both sites, with the enrichment factors ranging in 143-1202. Element-As were slightly enriched, with the enrichment factors ranging in 31-37. The element-V, Cr, Mn, Co, Ni, Cu, Ba were from the soil source in both sites, with the enrichment factors ranging in 0.8-8.(4)Principal component analysis and cluster analysis showed that the industrial emissions and coal combustion, vehicle exhaust and fugitive dust are the main sources of heavy metals in the suburban site, contributing by 32%, 21.1% and 16.5%, respectively.The coal combustion, industrial process, vehicle exhaust and the fugitive dust are the main sources of heavy metals in the urban site, contributing by 42%, 31.8% and 9.1%, respectively.(5)The PMF analysis showed that industrial emissions, coal combustion,vehicle exhaust and fugitive dust are the main sources of heavy metals in the rural site, contributing by 33.6%, 31.7%, 23.7% and 9.1%, respectively. The coal combustion, vehicle exhaust, fugitive dust and industrial process are the main sources of heavy metals in the urban site, contributing by 40.5%, 39.3% , 10.7% and 9.4%, respectively.(6)Health risk assessment results indicated that the values of non-carcinogenic risk were 1.5E-07～3.3E-03, below the threshold range (0-1) in both sites. The carcinogenic risk of Cr was 1.1E-06 in rural site, exceeded the carcinogenic risk threshold range (10-6-10 4). The values of carcinogenic risk were 1.1E-07～8.6E-07,below the threshold range in urban site, at an acceptable level.