Physical And Chemical Characteristics,isotope Source Tracer And Health Risk Assessment Of PM₁ In Typical Cities Of Sichuan Province

PM1 have smaller particle size,larger specific surface area,stronger ability to carry toxic and harmful pollutants and greater harm to climate and health compared with PM2.5.Related studies show that PM1 accounts for more than 80%of PM2.5,and PM1 has gradually become the main factor of atmospheric fine particulate pollution.PM2.5 have been reported in many literatures worldwide,but the systematic study of PM1 is rare.In particular,the distribution characteristics,physicochemical characteristics,sources,and effects on human health of PM1 in cities with different functional areas and different industrial structures are still unclear.Based on the above problems,the physical and chemical characteristics,sources and health risks of PM1 in typical cities of Sichuan Province(e.g.Chengdu and Panzhihua),were studied in this study.The mass concentration,micro-morphology,trace element,water-soluble inorganic ions and C?Pb?Tl source of PM1 were studied,and the similarities and differences of PM1 in two different functional areas were compared.The main findings and conclusions are as follows:(1)The mass concentration of PM1 in Chengdu is higher than that in Panzhihua City.The mean annual mass concentration of PM1 in Chengdu is(46.50±22.68)?g/m³;and 1.47 times that of Panzhihua.The mean annual mass concentration of the two cities was 3.91 times and 2.66 times of the background site,respectively.The difference between the two cities is due to the poor atmospheric diffusion conditions in Chengdu compared with Panzhihua.The types of particulate matter in PM1 from Chengdu are mainly:fly ash,soot,S-Ca particles.Except for the above types,the Si-Al particles and the metal particles are observed in PM1 from Panzhihua City.The results of trace element analysis showed that the whole trace elements in PM1 from two cities were higher in autumn and winter season than spring and summer.(2)The results of WSIIs show that NO₃^-,SO₄^2-,NH₄⁺are the main three ions in PM1 from Chengdu and Panzhihua,which account for 90.90%and 79.75%of WSIIs,respectively.The calculation results of WSIIs balance and the form of ion occurrence show that the WSIIs in PM1 from Chengdu are weak alkaline,while Panzhihua City is alkaline.Ammonium salts in PM1 from Chengdu and Panzhihua are mainly in the form of NH4NO3 and(NH4)2SO4.The ratio of NO₃^-to SO₄^2-in PM1 from Chengdu is greater than 1(except summer),and is dominated by mobile sources,while the ratio of NO₃^-to SO₄^2-in PM1 from Panzhihua is less than 1 and is dominated by fixed sources.In terms of SOR and NOR,Chengdu is higher than Panzhihua,and there are seasonal differences in the formation of SO₄^2-.Chengdu has the highest SOR in winter,which is related to heterogeneous reaction,while Panzhihua has the highest SOR in summer,which is related to homogeneous oxidation reaction.NOR in PM1 from Chengdu and Panzhihua is negatively correlated with temperature,which is mainly due to the evaporation loss of ammonium nitrate at high temperature.(3)The OC and EC in PM1 form Chengdu and Panzhihua have the same trend,that is,the range of EC variation in each season is small,indicating that the emission source is relatively stable,and mainly primary emission source;The range of OC variation in each season is large,indicating that OC is mainly the result of the interaction of primary and secondary sources.The estimation of SOC in PM1 shows that the seasonal concentration trends in Chengdu and Panzhihua are as follows:summer>winter>spring>autumn,N point:winter>spring>autumn,and H point:spring>autumn>summer>winter.The summer sunshine time is long and strong,which is beneficial to the photochemical reaction in Chengdu.(4)The EF showed that most of the elements in PM1 of Chengdu and Panzhihua were from anthropogenetic sources.(5)The TC accounted for 18.13%and 25.67%of the PM1 mass concentration in Chengdu and Panzhihua,respectively,and the carbon component has become an important component of the PM1 in Chengdu and Panzhihua.Therefore,it is necessary to accurately determine the source of C in PM1 and calculate its contribution.The C isotope tracer technique has been used to quantitatively analyze the source of C in PM1.The results show that the main sources of C in PM1 from Chengdu are vehicle exhaust(52.4%),combustion of C3 plants(26.2%),coal burning(16.2%)and combustion of C4 plants(8.1%).However,the C source in PM1 from Panzhihua was mainly from vehicle exhaust(47.8%),coal burning(22.4%),C3 plant combustion(21.6%)and C4 plant combustion(8.1%).(6)Lead is the only heavy metal with specified concentration limit in ambient air quality standards(NAAQS,GB3095-2012)in China.Moreover,our study found that the EF values of Pb in PM1 from Chengdu and Panzhihua are moderate to high enrichment.Therefore,it is particularly important to accurately identify the source of lead in PM1.Only the concentration of lead and chemical or mineralogical information is not enough to accurately find the source of lead pollution.In our study,the source of lead in PM1 is quantitatively analyzed by using pb isotope tracer technique.The results show that the Pb of PM1 in Chengdu mainly comes from automobile exhaust,coal-burning dust and building dust are 52.3%-71.5%,28.5%-47.7%.Four seasons of Panzhihua,smelting dust contributed the most,followed by vehicle exhaust,and coal burning contributed the least,and their contribution rates were 45.4%,35.7%,and 18.9%,respectively;Lead isotope tracer analysis also shows that the contribution of smelting dust and coal burning at N point to Tl in PM1 is83.3%-89.0%and 11.0%-16.7%,respectively,while the contribution range of smelting dust and coal burning at H point to Tl in PM1 is 85.6%-91.7%and 8.3%-14.4%,respectively.This study shows that the contribution of iron and steel smelting activities to Tl is very significant.(7)Arsenic and Cd in PM1 from Chengdu have carcinogenic risk for adults and children,and the risk is that adults are larger than children,Cadmium has carcinogenic risk for adults.Arsenic,Cd and Cr(?)in PM1 from Panzhihua have carcinogenic risk to adults,and As and Cr(?)have carcinogenic risk for children.