Characteristics And Source Of Platinum Group And Heavy Metal Elements In Atmospheric Fine Particles (PM_2.5) In Guiyang City

Automobile exhaust dust is one of the main sources of atmospheric fine particulate matter(PM_2.5).The concentration of platinum group elements of Pt,Pd and Rh（PGEs）is usually 1-3 orders of magnitude higher thant that in common dusts,hence it is considered as an important parameter for the study on the composition and source of atmospheric particulate matter.Guiyang City is located in the center of a large area of low-temperature mineralization zone in the southwest of China,enriching in mineral resources.It is an important coal base,and the industrial activities of coal combustion,mineral mining and metal smelting emit a large amount of particulate matter with aboundance of As,Zn,Mn,Co,Ni and V,which makes the source of air pollution in Guiyang City quite different from other cities.In order to study the characteristics,potential sources and health risks of PGEs and heavy metals in PM_2.5 in Guiyang City,the PGEs’ detection and analysis methods in atmospheric fine particles were optimized by screening the sampling filter membrane and reducing the blank value of the sampling filter membrane.Simualtaneously,from August 2018 to July 2019,atmospheric PM_2.5 samples（n=317）were systematicly collected by using Wuhan Tianhong sampler and URG 3000 K multi-function sampler.The concentrations of PGEs and ten heavy metals（Pb,Cd,Cr,As,Zn,Mn,Co,Ni,Cu,and V）in PM_2.5 were measured by using inductively coupled plasma mass spectrometry（ICP-MS）method.The characteristics and potential sources of PGEs in atmospheric fine particles were discussed.The distribution,potential sources,and health risks of 10 heavy metals were elucidated by using PMF（positive definite matrix factor analysis）model and HMHR（health risk assessment model）.The following is the major results:1.The PM_2.5 concentrations in Guiyang City were in the range of 11～156 μg/m³,and the daily average value of PM_2.5 was（60±26）μg/m³,which is lower than the national secondary air quality standard（75 μg/m³）and the US environmental protection agency（US EPA）recommended value（65 μg/m³）.The seasonal trend of PM_2.5 concentration in Guiyang City was in the order of winter> autumn> spring> summer.2.The results showed that the blank of PGEs and trace elements in P mabrane was the lowest,with concentraitons of Rh,Pd and Pt were（0.019±0.022）,（0.478±0.012）and（0.039±0.013）ng,respectively.The concentrations of 4 kinds of low field strength elements and 10 kinds of other trace elements in C mabrane were high,reaching up to（129.9±59.78）and（80.84±23.14）ng,respectively.Similarly,high concentrations of 6 platinum group elements,5 transition metal elements,and 7 high field strength elements in W mabrane were observed,which are（4.392±0.901）,（389.2±123.8）,and（80.48±5.095）ng,respectively.After treatment with aqua regia,the average efficiency of the platinum group and trace elements of the quartz filter membrane（W′）was greater than 60%,among of which efficiency of 9 trace elements such as V,Pb,As,U was 10%-30%.Our results indicated that the blank of W mabrane can meet the requirements for the collection and analysis of platinum group elements and trace elements in PM_2.5.And P can be directly used for the collection and analysis of platinum group elements and trace elements in PM_2.5.3.The concentrations of PGEs in PM_2.5 in Guiyang city were in order of winter> autumn> spring> summer.The average annual concentrations of Pd,Pt and Rh were 16.04±4.15,5.84±1.91 and 1.46±0.37 pg/m³,respectively.The isotopic composition of Pd and Pt in PM_2.5 in Guiyang was consistent with the isotopic composition of Pd and Pt in the coating of automobile exhaust catalyst.The linear correlation analysis of Pd,Pt and Rh showed that PGEs in PM_2.5 in Guiyang derived from automobile exhaust catalyst.4.The sources of PGEs in road dust and urban dust were mainly from automobile exhaust catalysts,and a positive correlation of PGEs concentration was observed between road dust and traffic flow.The concentration of PGEs in PM_2.5 in the tunnel is consistent with the mass concentration of PGEs in atmospheric PM_2.5 in Guiyang City.Natural soil dust,coal combustion,steel processing,and metal smelting in Guiyang City were not the release sources of PGEs into the atmosphere.The major source of PGEs in atmospheric PM_2.5 was automobile exhaust catalyst.5.The 10 heavy metals in PM_2.5 show that the concentrations of Pb were lower than that at night,while the concentrations of Ni,Mn,Zn,and Cu were higher than that at night.PMF analysis showed that the main sources of the ten heavy metals in PM_2.5 were traffic（39%）,coal combustion（37%）,industrial metallurgy（14%）and soil dust（10%）;HMHR results showed that Cd and Mn had certain non-carcinogenic health risks for children,while As and Cr had high cancer risks threshold of ILCR（incremental lifetime cancer risk）,posing a certain degree of carcinogenic risk to people.