| Fine particulate matter(PM2.5)has been shown to have pronounced effects on human health,regional air quality,and global climate.Particulate organic matter is the major constituent of PM2.5,accounting for approximately 1/31/2 PM2.5 mass.It has been reported that organic matter could change radiation intensity by increasing scatter and reflection of light,resulting in atmospheric visibility reduction.Nevertheless,the temporal and spatial variation of organic matter was rarely investigated in China.Therefore,the present study aims to measure the detailed chemical composition of organic species in PM2.5 and study the spatiotemporal variations of sources contributing to organic carbon.PM2.5 samples were collected simultaneously at three sites in Wuhan in industrial area?ID?,downtown Wuhan?DT?,and Wuhan botanical gardens?BG?.The major constituents of PM2.5 were found to be organic matter and secondary inorganic ions,totally explaining 47.1%?56.9%,and 57.2%of PM2.5 mass at ID?DT and BG site,respectively.The concentration of major constituents of PM2.5.5 varied seasonally across all sites;specifically,sulfate,nitrate and organic carbon varied most strongly during spring,followed by summer and fall.Organic carbon varied the most across sites for all seasons,which is attributable to large differences in local industrial emissions.A total of 125 organic species in PM2.5 were identified and quantified,including27 polycyclic aromatic hydrocarbons?PAHs?,31 n-alkanes,23 hopanes and steranes,32 fatty acids and 12 monosaccharide.The highest concentration of PAHs observing in winter could be ascribed to cold-ignition of vehicles.The average CPI value?1.1±0.2?and relatively lower Cmax(C23,C24)for n-alkanes indicate the predominance of anthropogenic sources in Wuhan.Hopanes and steranes acted as molecular markers and are mainly produced by fossil fuel combustion.The highest annual concentration of hopanes and steranes was found at DT site?13.0±8.4 ng/m3?,confirming the significant vehicle emissions at this site.Levoglucosan can be utilized as a molecular tracer for biomass burning.Extremely high values of levoglucosan?the maximum value:2794.3 ng/m3?were observed at all sites,and 72h backward trajectory analysis revealed that regional-range transport?from Jiangsu?Anhui and Henan?of biomass burning emissions mixed with locally produced pollutants could be the main cause of serious haze pollution event in fall of Wuhan.Using the molecular markers-CMB model,the contributions of primary sources to organic carbon?OC?in PM2.5 were calculated.The major primary sources contributing to OC were vehicle emissions?38.1%±8.3%?,coal combustion?7.0%±6.2%?,meat cooking?3.0%±1.6%?,biomass burning?3.0%±1.0%?,and vegetative detritus?0.8%±0.6%?.Secondary organic carbon?SOC?was estimated based on EC-tracer method,and the percentage of SOC to total OC varied from16.2%63.7%with an average of 37.9%.Additionally,the contributions of primary sources plus secondary inorganic ions including sulfate,nitrate,and ammonium,accounted for 83.4%±9.8%of PM2.5 mass on a yearly average basis over all site.Secondary inorganic ions contributed the most to PM2.5 mass,accounting for 24.2%±3.1%of PM2.5 mass.Vehicle emissions were the second largest contributors to PM2.5 mass,averaging 25.5±11.6?g/m-3 and accounting for 20.0%±4.0%of PM2.5 mass.Mineral dust was the next major contributor to PM2.5(average 16.8±9.6?g/m-3)and have homogenous concentrations across the sites during springtime due to regional dust storms,but had much higher concentration at ID during the summer and fall.All these sources had large spatial variations across the three sampling sites.Vehicle emissions had the largest impact at DT,coal combustion,mineral dust and industrial emissions had the largest impact at ID.In contrast,regional sources,such as secondary sulfate,nitrate and ammonium contributed equally to the PM2.5.5 mass in sub-areas of Wuhan. |
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