Study On Chemical Characteristics And Source Apportionments Of Fine Particulates In The Typical Cities Over The Central And Eastern China

With the rapid development of economy and urbanization,the atmospheric pollution continues to deteriorate over the central and eastern China.Atmospheric particulates,especially fine particulates PM2.5 have negative impacts on air quality,climate changes and human health.In this study,the PM2.5 off-line samplings were carried out from December 2014 to November 2015 at five representative megacities,namely,Beijing,Nanjing,Wuhan,Taiyuan and Guangzhou in the central and eastern regions of China.Firstly,the PM2.5 pollution characteristics of mass concentrations were analyzed.Secondly,the concentrations,seasonal and spatial variations of water soluble inorganic ions and carbonaceous species were discussed.Finally,by the method of principal component analysis(PCA)to analyze sources of water soluble inorganic ions and carbonaceous in PM2 5,it aimed at providing theoretical basis for the prevention of atmospheric pollution.The main results were as follows:According to the standard level Ⅱ of National Ambient Air Quality Standards(GB 3095-2012,75μg/m3),the PM2.5 pollution was most serious at Nanjing and Taiyuan,followed by Wuhan and Bejing,and the lightest at Guanzhou.The PM2.5 pollution levels were given priority to with good weather and light pollution,with the total percentages of 67.7%～81.1%.Emission sources,regional atmospheric transports and meteorological conditions resulted in significant seasonal differences in PM2.5 concentrations.The daily PM2.5 mass concentrations in winter and(or)autumn fluctuated greatly and the higher PM2.5 annual concentrations were observed in winter,while the PM2.5 daily concentrations tended to be stable.Water soluble inorganic ions were the main chemical components of PM2.5.The total water soluble inorganic ions concentrations in Beijing,Nanjing,Taiyuan,Wuhan,and Guangzhou accounted for 38.5%,44.3%,49.0%,46.7%,and 32.2%of PM2.5 mass concentrations,respectively.Sulfate,nitrate,and ammonium(SNA)were the most sufficient ion species,accouting for 74.6%(Beijing),82.0%(Nanjing),73.9%(Taiyun),85.2%(Wuhan),86.2%(Guangzhou)of the total water soluble inorganic ions.The higher percentages of SNA in PM2.5 were discovered in summer and autumn,while lower percentages in winter and spring.The fine particulates in Beijing and Guangzhou were electrically neutral,while alkaline in Nanjing and Taiyuan and acidic in Wuhan.The ammonium concentrations in Taiyuan were high enough to neutralize sulfate,nitrate and chloride completely,while ammonium in other four cities was relatively lacking,among which Nanjing and Wuhan ammonium could only neutralize partial sulfate.Mobile source made the dominant contribution to Beijing PM2.5 pollution.Mobile and stationary emissions contributed equally to Nanjing PM2.5 pollution.Stationary emissions dominated in fine particle pollution in Wuahn,Taiyuan and Guangzhou.As one of the most important components in PM2.5,the annual concentrations of total carbon aerosols(TCA)in Beijing,Taiyuan,Wuhan,and Guangzhou were 24.73μg/m3,34.79μ/m3,26.17μ/m3,and 16.85μg/m3,accounting for 34.4%,36.6%,30.3%,and 26.9%of PM2.5 mass concentrations,respectively.The annual average concentrations of organic carbon(OC)were 1.9 to 2.3 times that of elemental carbon(EC).The highest OC and EC concentrations were observed in winter,while lowest in summer.Linear correlation coefficients showed that OC and EC had identical sources in Bejing,Taiyuan and Wuhan,while the origins of OC and EC in Guangzhou were complicated.The average OC/EC ratios in four cities were greater than 2.0,indicating the existence of secondary organic carcon(SOC)pollutions.The highest SOC annual concentration observed in Taiyuan was 10.9μg/m3,accounting for 69.0%of OC concentrations.The lowest SOC concentration observed in Guangzhou was 4.0μg/m3,with percentage of 54.0%.Due to emission sources and meteorological conditions,the seasonal variations of SOC concentrations were inconsistent with that of SOC/OC ratios.Source apportionments were carried out according to the concentrations of water soluble inorganic ions and carbonaceous species by the means of principal component analysis(PCA).The main sources of water soluble inorganic ions in Beijing were secondary pollution,biomass burning and dust,and carbonaceous species mainly originated from biomass burning,coal combustion and vehicle exhaust.In Nanjing,water soluble inorganic ions in PM2.5 were mainly from coal combustion,vehicle exhaust,biomass burning and dust.In Taiyuan,the water soluble inorganic ions were mainly from secondary sources,biomass burning,coal combustion,dust,farming and livestock,and carbonaceous species originated from biomass and coal combustion,gasline vehicle exhausts.In Wuhan,the main sources of water soluble inorganic ions in PM2.5 were secondary pollution,coal and biomass burning,dust,and carbonaceous species were mainly from coal and biomass burning,gasline vehicle exhausts.In Guangzhou,water soluble inorganic ions were mainly from secondary pollution,biomass and coal combustion,dust,and carbonaceous species were mainly from vehicle exhaust,coal and biomass burning.Therefore,it is crucial to improve the quality of atmospheric environment in the central and eastern regions by replacing the coal with clean energy,controlling the growth of motor vehicle ownerships and improving the quality of fuel,strictly forbidding to burn biomass such as straw and expanding green vegetation coverage.