Chemical Composition And Source Identification Of Atmospheric PM_2.5 And PM₁₀ In Wenjiang,Chengdu

This article conducts research on atmospheric particulate matter PM_2.5 and PM₁₀in Wenjiang,Chengdu.It is hoped that by measuring the concentrations of water soluble ions and inorganic elements in PM_2.5 and PM₁₀,the sources of ions and elements in the atmospheric particulate matter will be explored,and a scientific basis and data support for the prevention and control of atmospheric pollution in the region will be provided.The paper selected medium-flow atmospheric samplers to collect atmospheric samples at the Wenjiang campus of Sichuan Agricultural University from July 2017to May 2018.The mass concentration of the particulate matter was determined by a weighing method.At the same time,an ion chromatography was used to determine the concentrations of water-soluble ions in the samples.After the sample is pretreated by the mixed acid digestion method,the concentrations of inorganic elements in the samples were measured by an inductively coupled plasma emission spectroscopy and an inductively coupled plasma mass spectrometry,and the pollution characteristics and distributions of water-soluble ions and inorganic elements in the particles were studied.The specific research conclusions are as follows:1)During the sampling period,the average annual mass concentrations of PM_2.5and PM₁₀ in Wenjiang were 64.65μg/m³ and 106.83μg/m³,respectively,which exceeded China’s secondary air quality standards（GB3095-2012）.There are obvious seasonal changes of the mass concentrations,with the highest values in winter,the second in spring and autumn,and the lowest in summer.Mass concentrationsare negatively correlated with wind speed,relative humidity,and temperature.2)The main water-soluble ions in PM_2.5were NO₃^-,SO₄^2-,NH₄⁺and Cl^-,while the main water-soluble ions in PM₁₀were NO₃^-,SO₄^2-,NH₄⁺and Ca²⁺.NO₃^-is the ion with the highest concentrations in PM_2.5 and PM₁₀,followed by SO₄^2-,NH₄⁺.The sum concentrations of NO₃^-,SO₄^2-and NH₄⁺accounted for 87.31%and 83.75%of total concentrations of ions.The seasonal trends of the concentrations of water soluble ions are same as those of the particle mass,with the highest levels in winter and the lowest in summer.The change of NO₃^-/SO₄^2-reflects that the atmospheric particulate pollution in spring,autumn and winter in Wenjiang is mainly caused by mobile sources,which isautomobile exhaust pollution.3)The primaryinorganic elements in PM_2.5 and PM₁₀ in the study area are Ca,Mg,Fe,Cr,Zn and Ti.Except for Cr,the average concentrations of poisonous heavy metals are lower than the limits of the national standards（GB3095-2012）.The mass proportions of different elements in PM_2.5 and PM₁₀ in the four seasons are different.The particle size distributions of Ca,As,Sb,and Tl are also different in different seasonal samples.Mg,Fe,Cr,Zn,Ti,Cu,Pb,Mn,Ba,Ni,V,Se,Sn,Co,Mo,Cd and Be are more easily enriched on fine particles in all samples.4)Correlation analysis showed that in PM_2.5,except for SO₄^2-and Mg²⁺,F^-,the water-soluble ions were positively correlated with each other,and in PM₁₀,9water-soluble ions were positively correlated.In PM_2.5,except for Fe,As,Sn,Sb and Be,the correlations between inorganic elements are good;in PM₁₀,except As,Sn,Sb and Be,the correlations between inorganic elements are also good.5)Principal component analysis showed that the two main sources of water-soluble ions in PM_2.5 were fossil fuel combustion and surface dust,and the contributions of the variances were 53.28%and 15.79%,respectively.The two main sources of water-soluble ions in PM₁₀ were fossil fuel or biomass combustion and surface dust,and the contributions of the variances were 64.98%and 18.26%,respectively.The main sources of water-soluble ions in atmospheric particles in Wenjiang of Chengdu are fuel combustion and surface dust.The five main sources of inorganic elements in PM_2.5 were traffic sources,coal combustion,metal smelting,industrial dust and surface dust,and their contributions to variance were 50.77%,13.10%,11.12%,5.87%and 5.21%,respectively.The five main sources of inorganic elements in PM₁₀ were traffic source,coal combustion,metal smelting,iron and steel smelting,industrial dust,and their contributions to variances were 43.53%,14.83%,10.29%,7.40%and 5.55%respectively.The main sources of metal elements in the air particles in Wenjiang of Chengdu are mostly the pollution caused by human activities,including traffic sources,coal combustion,metal smelting,steel smelting,industrial dust and surface dust.