| Fine particulate matter(PM2.5)is the most harmful pollutant to human life and health in the atmospheric aerosol,the growth of its concentration has direct relation to the formation of haze in the city.The chemical composition of PM2.5 is extremely complex,and it is recognized that carbonaceous aerosols and water-soluble ions are the main components of the chemical composition.By studying the pollution characteristics of them,we can compare the leading factors affecting the air quality in different seasons.And the source analysis of the dominant factor is carried out by the isotope method.It is hoped that the contribution of various sources of pollution to Urban Haze can be quantified.In this paper,Xuzhou,one of the central cities of the Yangtze River Delta,is selected as the research object based on the air quality for Xuzhou in the final echelon of Jiangsu Province for many years.In the background of the obvious improvement of air quality in most cities in China especially in the polluted areas,the atmospheric PM2.5 concentration in Xuzhou is still rising.It is urgent to solve the problem of air pollution in Xuzhou.It is important not only for improving the quality of life of the local people in Xuzhou,but also for reducing the influence of Xuzhou’s air masses on the neighboring cities.In this study,we collected atmospheric PM2.5 samples from four seasons of 2016,and analyzed the seasonal variation characteristics of organic carbon(OC),elemental carbon(EC),water-soluble organic carbon(WSOC)and water-soluble inorganic ions(WSIIs)in the samples and their correlation with PM2.5.Combined with backward trajectory model,the influence of foreign air mass transfer on air quality in Xuzhou was analyzed.In terms of source apportionment,principal component analysis model was applied to analyze the possible sources of ionic components in PM2.5,and a Bayesian isotope mixing model was used to quantitatively analyze the nitrogen contents in the atmosphere.The main conclusions are as follows:(1)PM2.5 concentration in Xuzhou city was at a high level throughout the country.The average concentration of PM2.5 during the whole sampling period was 115.8 ± 67.4 μg·m-3,this value was 3 times than the national average annual concentration secondary standard(35μg·m-3).The most serious pollution happened in winter and summer,the proportion of haze days to the whole sampling days were 90%and 100%,respectively.It showed the importance of the study on the atmospheric PM2.5 pollution in winter.Meteorologic conditions on the beneficial effects of PM2.5 mainly accumulated for low temperature and low humidity,and the wind from the southeast and northwest would bring a lot of pollution.(2)The variation trends of OC,EC were basically the same as that of PM2.5,the seasonal variation was winter>(spring,autumn)>summer.OC and EC with PM2.5 as well as OC and EC have good correlations especially in winter and autumn,indicated the increase of PM2.5 concentration depended largely on the concentration of carbon containing components,and the source of OC and EC was relatively stable.(3)Water soluble organic carbon(WSOC)could be used as an ideal characterization substance for secondary organic aerosols(SOA).The average concentration of WSOC was highest in winter(9.9 ±5.4 μgC·m-3),followed by the values in spring and autumn,and the lowest value in summer was 3.0±1.2 μgC·m-3.Through the correlation analysis between WSOC/EC with RH and O3,it is concluded that high humidity in winter promoted the secondary generation of WSOC,while photochemical reaction was the main reason for WSOC generation in autumn.(4)Secondary inorganic ions(SO42-,NO3-and NH4+,named as SNA)were the key components of water soluble ions,which accounted for 84%of the total water soluble ions(TWSIIs).The proportions of SNA to TWSIIs and PM2.5 increased with the increase of pollution degree,indicating the important contribution of SNA to air pollution.The dominant pollution ions were nitrate and sulfate in winter and summer,respectively.And the average concentrations of nitrate in spring and autumn were slightly higher than those of sulfate.(5)The results of factor analysis showed that the main pollution in winter in Xuzhou from secondary transformation,followed by biomass burning;the pollution in summer was mainly caused by the secondary transformation of fossil fuel and agricultural emissions,followed by sea salt and mineral dust;The sources of spring and autumn were similar,mainly influenced by biomass combustion and secondary transformation,and mineral dust also the contributor.The quantitative analysis of nitrogen content in winter indicated that the NOx emission from fossil fuel was the main cause of PM2.5 pollution.Therefore,controlling the N emissions from coal combustion and transportation is the key to control air pollution and reduce haze in Xuzhou. |
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