| PM2.5 is one of the global air pollutants,which can lead to reduce of visibility and is serious harmful to human health.At present,most of the previous studies of atmospheric particulate matters were focused on the Beijing-Tianjin-Hebei region,the Pearl River Delta and inland areas.Few studies were about the characteristics of PM2.5 in the Yangtze River Delta Region,which located at the typical subtropical seasonal climate areas and has become the fourth largest haze area in China.Therefore,Hangzhou,a large city located in the Yangtze River Delta region,was selected as the study area,and PM2.5 was collected from 2014 to 2016.Then,physicochemical characteristics and toxicity of PM2.5 were analyzed,meantime the correlation between gaseous pollutants and fine particle composition were discussed.The difference of PM2.5 in different seasons and pollution degree were investigated,and human lung bronchial cells BEAS-2B were used to analyze the toxicity difference.The object of this paper is to provide a theoretical basis for the management and pollution control of PM2.5 in this region of Hangzhou City.The main results were as follows:?1?During the sampling period,the concentration range of PM2.5 in this region of Hangzhou was 21-290 ?g/m3,and main weather condition was good and light polluted,and the average concentration of PM2.5 were higher in the winter and lower in the summer.The results of correlation analysis showed that the concentration of PM2.5 had a high homology and similar change with SO2,NO2?the correlation coefficients were 0.55 and 0.62?,while had a poor homology and different variation with O3?correlation coefficient was-0.14?.The second components NO3-had a positive correlation?R2=0.50?with gaseous precursors NO2,while the correlation between SO42-and SO2,SO42-,NO3-,SOC and O3 were poor,which indicated they had synchronized changes.?2?The PM2.5 samples were observed by electron microscope,typical particles mainly included soil dust,fly ash and deformed coal fly ash,soot and soot aggregates,second particles.It showed that with the increase of the pollution degree,the PM2.5 particles generated obviously and became large particles simultaneously,especially in the spring and winter PM2.5 were more likely to generate large particles.According to the results of factor analysis of chemical composition,the main sources of PM2.5 in this region of Hangzhou City were second source,coal combustion,vehicle emissions,dust of soil,road and construction,biomass burning and long-distance transportation.The PM2.5 in the summer was more affected by the coal combustion while in the winter it was automobile exhaust.During sever PM2.5 pollution period,vehicle exhaust was the most important contributor,and second source and coal contribution were also important sources,while the impact of biomass burning and dust of soil and road were relatively small.?3?Water soluble ions were the main component in PM2.5 in this region of Hangzhou City,and the average proportion in PM2.5 was 45.43125.75%.SO42-,NO3-and NH4+ were the main water soluble ions.Cl-and K+ affected by the combustion of biomass,were higher in the autumn and winter,and lower in the spring and summer;NH4+ influenced by typical agricultural sources,was higher in the autumn than other seasons;the concentrations of SO42-and NO3-were higher in the winter and spring than in the autumn and summer,which mainly influenced by the conditions of gas-solid reaction and concentration of gaseous precursor.NH4+ was first combined with NO3-and generated NH4NO3 in the spring,summer and autumn,then the remainder part combined with SO42-and generated?NH4?2SO4,however it was opposite in winter.The concentration and percentage of total water soluble ions increased with the pollution degree,and the concentration of NO3-increased more than SO42-.In the haze forming process NO3-increased with a proportion of 9.09%,even became the most abundant water soluble ions during severe pollution period.?4?The proportion of OC and EC in PM2.5 was 18.21 14.22%,3.34± 1.35%respectively;the average percentage of SOC in PM2.5 accounted for 13.20±3.68%,showed that this region of Hangzhou was sever influenced by second organic pollution.The concentration of EC showed no obvious seasonal difference,but TC,OC,and SOC were higher in winter and lower in summer.The concentration of OC increased with the pollution but its proportion declined,however the concentration of SOC increased while its proportion did not change significantly in sever pollution period,thus it meant the increasing content of SOC was the main reason of the increased concentration of OC during haze pollution.?5?The content of metals in PM2.5 was few,only accounted for 1.00±1.68%in PM2.5,and was a little higher in the summer than other seasons.The seasonal differences of different metals were influenced by sources,meteorological conditions and the combination of elements with fine particles.The effect of metals on the haze aggravated period could be ignored.?6?The results of cell exposure test showed that the higher the concentration of PM2.5 and the longer the exposure time,the greater the impact on cell viability.When the mass concentration of PM2.5 was similar,the water extraction from the summer samples might show a greater impact on BEAS-2B than that from the winter samples.In a word,the current PM2.5 pollution in Hangzhou City is not optimistic,and mainly influenced by second source,coal combustion and vehicle emissions.Results of this paper showed that the direction of further PM2.5 pollution governance in Hangzhou was motor vehicle exhaust control,meanwhile the control of coal sources can not be relaxed. |
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