| In recent years,due to economic development,the increase number of motor vehicles,and the advancement of urbanization,urban atmospheric pollution originating from PM2.5 has shown new characteristics.The main purpose of this study is to investigate the differences of ambient PM2.5 in mass concentration and chemical compositions in different seasons at Taiyuan,Shanxi Province,China and analyze their influencing factors.It is hoped to be helpful for taking corresponding measures to control air pollution and protect the public health.The main research contents include:?1?Based on the variation of the daily mean concentrations of atmospheric PM2.5 in four seasons from 2013 to 2014,the variation and factors affecting the mass concentration of PM2.5 in autumn were analyzed by using the single factor pollution index assessment,correlations analysis,and wavelet analysis.?2?PM2.5 samples were collected at a five-story building in Shanxi University using a medium-volume PM2.5 impactor from Jul.6 to Aug.20,2013?summer?,from Nov.21 to Dec.20,2013?winter?,from Apr.1 to Jun.5,2014?spring?and from Oct.4 to Nov.23,2014?autumn?.Metallic elements,water-soluble ions and OC and EC were detected by inductively coupled atomic emission spectrometer?ICP-AES?,ion chromatography,and carbon analyzers,respectively.?3?Atmospheric particles in three size range?0.5?1?m,1?2?m,2?4?m,respectively?were collected using a seven-stage May cascade impactor,resulting in four types of particle samples,i.e.,wintertime haze samples on Jan.8 and 9,2010,wintertime non-haze samples collected on Dec.29 and 30,2009,summertime haze samples on Jul.11 and 12,2010,and summertime non-haze samples on Jul.13 and 14,2010.The measurements were carried out on a SEM equipped with an Oxford Link SATW ultrathin window EDX detector,through which the size,morphology,and chemical composition of the individual particles were determined.Results showed that?1?the mass concentration of PM2.5 was the lagest and seriously overweight in winter,the second in autumn,the least in spring,diurnal variation regularity was not obvious in summer,and it was less than that before heating in the initial two weeks of heating.?2?The mean concentration of Zn,Pb,As,Cd and Cu were winter>autumn>summer>spring;SO42-,NO3-and NH4+ were the main components of water-soluble ions,the variation of them were consistent and had significant correlation;Cl-,K+ and Na+ were markedly increased in autumn;after heating,NO3-/SO42-was decreased,the concentration of OC and EC were increased and OC/EC was decreased?OC/EC in summer was the largest?.?3?There were significant differences between compositions of particles during winter haze and summer haze.Among PM1-2.5,the reacted mineral dust was the most abundant,and the sulfate-containing reacted mineral dust outnumbered the nitrate-containing ones in the winter haze particles,?C,N,O,S?-rich particles was the most abundant,and most reacted mineral dust contained nitrate in the summer haze particles.Among PM<1,fresh and aged?C,N,O,S?-rich particles were encountered frequently in the summer haze particles.These results suggested that the mass concentration and chemical compositions of PM2.5 in different seasons had different variation.They were strongly influenced by biomass and coal burning,coal burning emissions lead to the increase of EC was greater than OC,organic matter and NOx had more effect than SO2 on particulate matter.Meanwhile,with the generation of secondary aerosols during haze,fresh and aged particulate matter were often mixed together,indicating that high temperature and humidity and motor vehicle exhaust emissions also played significant roles in the formation of PM2.5.Thereafter,mass concentration of atmospheric PM2.5 is closely related to its chemical compositions.Therefore,we need to take appropriate measures to prevent and control pollution according to the change of natural and human factors. |
PDF Full Text Request