Pollution Characteristics Of Heavy Metals In Atmospheric Precipitation In Taiyuan

Precipitation is a significant way to remove pollutants from the atmosphere.Compared with other pollutants,heavy metals have been attracted a worldwide attention.On the one hand,the amount of heavy metal emissions is large and it is difficult to remove heavy metals from ecosystems.On the other hand,heavy metals are particularly dangerous to the human health and ecosystems due to their toxicity and bioaccumulation.In this study,precipitation samples were collected from January 2013 to December 2015 in Taiyuan,and the p H and electricity conductivity of samples were measured.Then concentration levels,wet deposition fluxes and sources of water-soluble ions and heavy metals were analyzed.Finally,the contamination levels of heavy metals were evaluated.The major conclusions were as follows:?1?The p H of precipitation varied from 4.34 to 8.72 with a volume-weighted mean of 5.43.The frequency of acid precipitation was 17.9%,16.7% and 21.9%,respectively,in 2013-2015.The total water-soluble ions in precipitation were in the range of 190.02-6072.46 ?eq·L^-1,with the mean level of 1155.96 ?eq·L^-1.Ca²⁺,NH₄⁺,NO₃^-and SO₄^2-were major ions and there were evident declining trends in the concentration of Ca²⁺?NO₃^-and SO₄^2-in the precipitation over the study period.?2?The concentrations of Cu and Cr were 77.02 and 45.54 ?g·L^-1,respectively.Except for As and Ba,other elements were mainly concentrated in the particulate phase,accounting for 56.1% to 98.5% of the total concentration.Si was the major component and accounted for 41.18% of the total concentration.?3?The wet deposition fluxes of heavy metals ranged from 8.43 to 358.75 mg·m^-2·day^-1 and they were the highest in the summer,followed by the autumn,winter,and spring.The wet deposition fluxes of heavy metals were affected by factors such as precipitation amounts and emission intensity.The wet deposition fluxes of dissolved heavy metals exhibited an increasing trend from 2013 to 2015.?4?Based on the correlation analysis and enrichment factor analysis,coal combustion and vehicle exhaust were main sources of nitrogen and sulfur in precipitation.Cu,Zn,As,Cd,Ba,and Pb were highly enriched,suggesting that these metals were seriously influenced by the anthropogenic activities.Results from positive matrix factorization?PMF?indicated that industry,coal combustion,vehicle emissions and crustal dusts were the major sources of heavy metals in precipitation of Taiyuan,with an average contribution of 50.47%,26.09%,13.59% and 9.85%,respectively.According to backward trajectory analysis,air masses from southeast and southwest direction contributed the most to the precipitation of Taiyuan,with the percentage of 39 and 27,respectively.The southern industrial areas should be paid more attention to.?5?The results of heavy metals pollution assessment showed that the contamination levels of Zn,Cu,As and Pb were slight,and Cd was at a moderate level of contamination.With regard to potential ecological risks,the 4)of a single heavy metal was less than 40,and the total potential ecological risk index was less than 150,indicating that the heavy metals pollution in precipitation of Taiyuan was at a slight ecological risk.