| Atmospheric fine particulate matter(PM2.5)pollution is one of the most serious environmental problems in China,which has a serious effect on climate,environment and human health.Source of PM2.5 is complex,and its source characteristics and evolution trend are hot issues in environmental science research and management.In recent years,Nanjing has already done some analysis in source apportionment and completed the previous stage(2012-2014)source apportionment of PM2.5.On this basis,this study focuses on the following three aspects of the work:(1)Based on PM2.5 chemical composition data for the whole year of 2015,analyze the source of PM2.5 in the second stage by PMF model;(2)Compare the results of the two stages and analyze the source evolution of PM2.5;(3)Study the regional transport characteristics of PM2.5 by the Lagrangian Backward Trajectory Model(HYSPLIT).The results of the study can provide scientific basis for studying the source of PM2.5 in Nanjing and other similar cities and can scientifically develop the control measures for haze pollution.The main results are as follows:(1)Source characteristics in 2015:the contribution rates of the main pollution sources of PM2.5 in Nanjing are motor vehicles(28.2%)>coal(26.8%)>industrial(21.6%)>dust(12.0%)>other sources(11.4%).Seasonal characteristics of sources:due to the needs of refrigeration and heating,coal-fired sources in the summer and winter occupies a relatively high proportion;due to the dry ground surface and wind,dust source in the spring and autumn accounted for a higher proportion,respectively 14.9%and 16.5%;As the decomposition rates of secondary aerosol is different in different seasons,SOA is minimum in summer and maximum in winter.Regional characteristics:the PM2.5 pollution level is high in Nanjing City Center(CCM)and industrial park(HGY);CCM is affected by the motor vehicle source,accounting for 30.5%;due to the large area of the park construction and road transport,the dust source contribution is high accounting for 17.6%;the sources of new urban areas(XL,PK,JN)are affected by both the urban and suburban area;the sources of the clean control point(GCH)mainly come from the peripheral cities,and PM2.5 concentrations is low,only 62ug/m3.(2)Source evolution characteristics:The characteristics of air pollution in Nanjing are changing from the traditional soot pollution to the combined pollution of coal and motor vehicles.In spring,autumn and winter,the concentration level of the indicated elements is lower than that of the previous stage while in summer,basically the same and it is the lowest in the whole year.In spring,the proportion of industrial sources,motor vehicles and dust sources increased,respectively 3%,2.3%and 1%and the proportion of coal and other sources decreased,respectively 3.2%and 3.1%,and the dust was more from soil dust than building dust;In summer the proportion of motor vehicle increased 4.7%,the other sources are reduced and coal source is basically the same;In autumn,the proportion of motor vehicle increased 6.7%,the proportion of industrial sources and dust sources increased slightly,repectively 0.7%and 0.8%and the proportion of coal-fired sources and other sources decreased,repectively 5.5%and 2.7%;In winter the proportion of industrial sources and motor vehicles increased 3.9%and 3.6%respectively and the proportion of coal-fired sources decreased significantly by 7.1%.In the city center,the sources of dust and coal both reduced 1.7%;In the clean point,the source structure is affected by Wuhu and Ma'anshan,and the proportion of industrial source increased 7.1%.(3)Regional transport characteristics:The sources in spring in Nanjing are mainly affected by the warm and humid air flowing from the north,like Beijing-Tianjin-Hebei region(20%)and the east,like the city of Shanghai and Hangzhou(41%);The source in summer is mainly affected by warm and humid air from the ocean(65%);The long-distance transmission air mass arrives in Nanjing in winter is mainly due to the dry cold air mass from Mongolia and Inner Mongolia(45%),and the heavy pollution in Nanjing is related to the effect of downdraft in winter.The heavy pollution incidents in January 2015 is not only related to the polluted air mass from the north,but also affected by the air pollution of the surrounding cities such as Shanghai and Hangzhou. |
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