Characterization And Sources Of PM_2.5 In Typical Areas In Wuhan

Particulate matters plays a key role in global climate change and human health.Regional haze has been frequently observed in China in recent decades,and PM2.5 is exactly identified as the primary pollutant for causing haze.Wuhan is located in central China,which is one of the most important industrial cities,and suffered a lot for atmospheric pollution.However,researches on PM_2.5 were mostly concentrated in cities like Beijing,Tianjin,Shanghai,few researches about PM_2.5 in Wuhan were done.For this crucial issue,measurements for PM_2.5 and its contents were conducted in typical areas?an industrial site and a botanical garden?.Chemical compositions of PM_2.5 were analyzed and sources of PM_2.5 were determined.Backward trajectories were investigated to imply the most important trajectories that contribute most to air pollution of Wuhan,and to provide fundamental knowledge for the control of air pollution in Wuhan.PM_2.5 samples were collected at an industrial site and a botanical garden in Wuhan from October 2011 to July 2012.Chemical characteristics and sources of PM_2.5 in different seasons were investigated.The annual mean concentrations of PM_2.5 were 179.7?g/m³ and 92.8?g/m³ at industrial site and botanical garden,respectively.In addition,seasonal variation for PM2.5 mass was similar,at two sites,the PM_2.5 concentrations in summer were found to be the highest one,followed by autumn?spring and summer.In the experiment period,98.2%and 87.5%of PM_2.5samples found to be unqualified for standards of air quality regulations.NH₄⁺in PM_2.5 samples collected in summer and winter were sufficient to react with SO₄^2-and NO₃^-.Nevertheless,it was not the case in spring and autumn,and Ca²⁺was the one that fill the gap for these periods.Fossil fuel burning was the most important contributor to carbonaceous aerosol both at industrial site and botanical garden.On the other hand,biomass burning contributed a small fraction of carbonaceous aerosol except that during spring at industrial site.As for botanical garden,biological emission was of more significance.Enrichment factor analysis showed that Al?Ti?V?Mn?Ba and Fe were mainly resulted from natural sources,and Cu?Zn?Pb?Cd were mainly caused by human activities,while Cr?As and Ni were effected by natural sources and human activities.Local emission sources and long-range transport pollutants had impacts on air quality in Wuhan.Positive matrix factorization?PMF?model was used to identify and quantify the main sources of PM_2.5.The results showed that secondary inorganic aerosol,biomass burning,vehicle emissions,metal melting,fugitive dust,coal combustion and residual oil combustion were the main sources of PM_2.5 in Wuhan.The importance of these major sources to PM_2.5 mass varied in different seasons.For industrial site,biomass burning?45.1%?and residual oil combustion?23.1%?was the largest contributor in spring and summer,respectively,while fugitive dust and vehicle emissions?56.2%??secondary inorganic aerosol?53.4%?was the dominant source in autumn and winter,respectively;as for botanical garden,vehicle emissions were the largest contributors both in spring and autumn,contributing 42.7%and 41.3%of total mass,respectively.Nevertheless,fugitive dust?27.3%?and secondary inorganic aerosol and biomass burning?57.4%?were found to be the main source of PM_2.5 in summer and winter,respectively.