Environmental Geochemistry Characteristic Of Atmospheric Particulate Matter In Baotou

With the rapid development of industrialization and urbanization,the particulate matter pollution problem is becoming more and more serious,which has great influence on air quality,human health and climate change.As primary pollutant of ambient air,the source of particulate matter is extremely complicated.The study of characteristics,sources and formation mechanism of the chemical composition in particulate matter is the basis for the prevention of particulate matter pollution.The PM₁₀,PM_2.5 and residential dust samples systematically collected in Baotou,a typical heavy industrial city in northern China.And the spatiotemporal distribution,source and mechanism of water-soluble ions,elemental carbon,organic carbon,heavy metals,rare earth elements and polycyclic aromatic hydrocarbons in particulate matter were studied.By means of stoichiometry,the response relationship between atmospheric pollutants and severe pollution processes was summarized.Tessier sequential extraction analysis was introduced into the environmental geochemical behavior of heavy metals and rare earth elements in residential dust,and the influence of iron and steel smelting on air pollution in Baotou was identified.The main findings are as follows:1.The chief pollutant of atmosphere in Baotou is mainly PM₁₀ in spring,O₃ in summer,and PM₁₀ and PM_2.5 varied in winter and autumn.The concentrations of PM_2.5,SO₂,NO₂ and CO in heating season were significantly higher than those of non-heating season,suggesting that coal combustion has a significant impact on air quality in Baotou.2.High concentration of Ca²⁺and Na⁺was found during dust storm days,while high concentrations of SO₄^2-,NO₃^-,NH₄⁺,K⁺and Cl^-were found during haze days.The cluster analysis,ternary diagram and PCA have a good agreement with each other,where crustal dust source,secondary particle source and the mixture of coal combustion,biomass burning and industrial pollution source were the main sources of WSIs in PM₁₀and PM_2.5.3.Correlations of OC and EC both in PM₁₀ and PM_2.5 with metrological conditions indicated that high wind speed and low relative humidity were beneficial for the removal of OC and EC.Pearson correlations and cluster analysis suggested that OC shared the same emission sources with SO₂ and CO from coal combustion and EC’s sources including vehicles exhaust and coal combustion both contributed to NO₂ as well.The OC concentration is mainly primary in warm months,while it appears secondary in cold months in Baotou.4.Concentrations of Si,Al,Fe,Ti and Cu in the dust storm days were much higher than those of haze and normal days,suggesting that the dust storm contributed significantly to the crustal elements in PM₁₀ and PM_2.5.The concentrations of Pb,Zn,Mn,As and Cd in haze days were significantly higher than those of normal days and dust storm days,indicating that the emissions from industrial sources contributed to these elements.The source of Pb,Cd and Hg in PM₁₀0 and PM_2.5 in Baotou were both natural and anthropogenic.The average enrichment factors of Pb,Cd and Hg in PM_2.5were significantly higher than those of PM₁₀,indicating that these elements were more easily concentrated on fine particles.5.Due to surrongding pollution and prevailing wind direction,the enrichment factors of Fe,Mn,Cr and V in residencial dust followed the order of Kundulun>Qingshan>Jiuyuan>Donghe.The enrichment factors of Al and Co were higher in Donghe district than those of other districts,which attrributed to the influence of large coal power plant and Beiliang demolition.The content of Fe,Mn,Cr,V,Zn and Cu decreases with the increase of the distance,especially for Fe,Mn and Cr,suggesting that the emissions from the steel smelting maybe the main source of these elements in residential dust.The results of risk assessment show that the risk of Hg and Cd is higher than other elements.6.The total concentration of rare earth elements in each speciation followed the order:residual fraction>Fe-Mn oxides fraction>organic matter bound fraction>carbonate fractions>exchangeable fraction.The Loess standardization distribution patterns of rare earth in the four study areas are all show high enrichment of light rare earth elements,which is in accordence with that of Baiyun obo iron ore.The concentration of∑REEs and enrichment factors of La,Ce,Pr and Nd decreased with the distance from the steel smelting enterprise,which showed that the steel smelting had a significant influence on the content of rare earth elements in the residencial dust samples.