Study On Chemical Compositions And Source Apportionment Of PM_2.5 During January 2017 In Chengdu

Located in the hinterland of Sichuan Basin,Chengdu is an important megacity in Southwest China.With the rapid development of industrialization and urbanization,urban anthropogenic emissions and the effects of special basin topography led to frequent air pollution in Chengdu,especially high concentrations of fine particulate matter PM_2.5 in winter.In order to understanding the characterize the fine particle pollution in Chengdu,this study conducted the field measurement with day and nighttime membrane sampling of PM_2.5 in Chengdu continuously from January 1 to 20,2017,and then investigated the main chemical components?water-soluble ions and carbonaceous materials?with the laboratory experiments.Futhermore,in order to explore Chengdu haze pollution sources,the WRF-CAMx-PSAT model was used to evaluate the contributions of Chengdu?CD?and its surrounding urban agglomeration Mianyang?MY?,Deyang?DY?,Suining?SN?,Ziyang?ZY?,Mianyang?MY?,Leshan?LS?as well as,the rest areas within the basin?ROB?and the outside of the basin?OOB?to PM_2.5 concentrations and chemical components in Chengdu.The modeling study also assessed the contributions of major sources of agricultural,industrial,power,resident,and transportation sectors to PM_2.5.5 concentrations in Chengdu.The Study results were concluded as follows:?1?Characteristics of PM_2.5 chemical composition change in Chengdu in January2017From January 1 to 20,2017,the averaged mass concentration of PM_2.5 was 127.1±59.9?g·m^-33 in Chengdu.The mass concentration of total water-soluble ions was 56.5±25.7?g·m^-3 in PM_2.5,and SO₄^2-,NO₃^-and NH₄⁺were the most important water-soluble ions respectively with mass concentrations of 13.6±5.5,21.4±12.0 and 13.3±5.7?g·m^-33 totally accounting for 85.6%of the water-soluble ions.The averaged mass concentrations of organic carbon?OC?and elemental carbon EC were 34.0 and 6.1?g·m^-3,respectively,accounting for26.8%and 4.8%in PM_2.5.Day and night PM_2.5.5 mass concentrations were 120.4±56.4 and133.8±64.0?g·m^-3,respectively,reflecting the high nighttime PM_2.5 levels for wintertime haze pollution in Chengdu,while the daytime concentrations of SO₄^2-,NO₃^-and NH₄⁺were higher than at night,which could be related to daytime high oxidizing for the secondary ions.The concentrations of Cl^-,K⁺,OC and EC increased significantly at nighttime,possibly due to nighttime coal and biomass burning increasing the nocturnal air pollutant emissions.The ion balance analysis in PM_2.5 shows that NH₄⁺is relatively excessive in Chengdu PM_2.5 in winter.The mean value of NO₃^-/SO₄^2-was 1.57,indicating the transportation mobile source exerting an more profound impact on PM_2.5 pollution.The correlation coefficients of OC and EC during day-and nighttime were 0.82 and 0.90?P<0.01?,respectively,reflecting the consistent sources of both OC and EC.The average value of ratio K⁺/EC was 0.31,and the correlation coefficient between K⁺and OC was 0.87?P<0.01?,indicating that biomass combustion had an important influence on Chengdu winter carbonaceous aerosols.?2?The contribution of air pollution source areas and types in and around Sichuan Basin to wintertime PM_2.5 and its chemical components in Chengdu.Analysis of regional contribution of air pollutants in Chengdu from January 2 to 19,2017shows that local source contributed 40.7%of PM_2.5.In the major cities in Chengdu's surrounding urban agglomeration,Ziyang contributed 19.7%,and Deyang?5.0%?and Mianyang?4.3%?to ambient PM_2.5 concentrations in Chengdu,while contribution rates from the rest areas of Sichuan Basin and the foreign region of basin were estimated with 10.9%and11.3%respectively.Among the regional sources of chemical component,NH₄⁺,EC and POA were mainly derived from local emissions,secondary pollutants SO₄^2-and SOA were mainly derived from regional air pollutant transport,and NO₃^-is simultaneously affected by local sources and regional air pollutant transport.The differences between source apportionment of the pollution and the clean period reveal that the air pollution was mainly caused by the local emissions and the air pollutant transport among major cities in Chengdu's surrounding urban agglomeration.The industrial,resident and transportation sectors were identified as the main sources of Chengdu PM_2.5 with the contributions of 44.3%,21.6%and 18.2%respectively.Among the components,the primary pollutants EC and POA are mainly from industrial s and residential sources,while the secondary pollutants NO₃^-and SOA are mainly from industrial and transportation sources.The industrial sources are their main contributors?63.3%?to SO₄^2-.Combined with the source contribution and the change of chemical composition concentrations,the formation of heavy pollution was caused by the local emission enhancement of POC and EC and also to the regional transport of secondary pollutants such as NO₃^-and SOA.Therefore,the control of pollutants in Chengdu should not only reduce local emissions,but also make the coordinated control over the basin region.