The Study On The Characteristics Of Polycyclic Aromatic Hydrocarbons And Heavy Metals In Fine Particulate Matter Of Shi Jing Shan In Beijing

In recent years,with the increasingly serious problem of urban atmospheric pollution,the study of the toxic substances of fine particulates in air has become a hot topic.Atmospheric toxic particulate pollutants such as polycyclic aromatic hydrocarbons?PAHs?and heavy metal components have caused great attentions.PAHs as persistent organic pollutants?POPs?have strong carcinogenic,teratogenic and mutagenic effects that are prevalent in the environment.In 1976,the International Agency for Research on Cancer?IARC?listed 15 PAHs as carcinogenic compounds.Benzo[a]pyrene is the first environmental chemical carcinogen that was discovered.Benzo[a]pyrene is often used as a representative of PAHs the total carcinogenic PAHs 1-20%due to its strong carcinogenicity.Similarly,heavy metals such as As,Cr,Cd,Ni,and Pb in particulate matter have significant hazards to the human body.In this study,16 priority PAHs released by the US Environmental Protection Agency and 8 toxic heavy metals were taken as research objectives,and the fine particulate samples were collected from January to December in 2016,the distribution characteristics and sources of PAHs pollution and heavy metals were studied in the atmosphere of Beijing,and the relationship between the change of PM_2.5 concentration and economic development in Beijing was analyzed to explore their intrinsic relationship.The results showed that the concentrations of PAHs in spring,summer,autumn and winter were 32.93±15.19,17.77±8.08,31.61±12.67 and 78.06±40.97 ng m^-3,respectively.The concentration of c-PAHs and nc-PAHs were 18.50±17.72 and21.55±8.79 ng m^-3,respectively.The concentration of c-PAHs in winter was the highest reach to 43.36 ng m^-3.In addition,the size distribution pattern changes of PAHs are also widely,more content in 0.2-0.5?m?32.4%?and 0.5-1.0?m?32.9%?particle size,The contents of heavy metals in PM_2.5 were as follows:Ca>Al>Fe>Mg>Ti>Zn>Mn>Pb>V>Ba>Cu>Cr>Ni>Sb>As>Co>Cd,toxic heavy metals Zn,Pb,Cu,Mn,As,Cr,Ni and Cd are mainly present in the 0.2-1.0?m?78.5%?.the seasonal trends are:winter>autumn>spring>summer.We studied the sources of PAHs in PM_2.5 by the characteristic ratio method.From the results of source analysis,the fuel combustion and traffic emissions are the main sources of PAHs in particulate matter.The effect of meteorological factors on PAHs concentration in PM_2.5 was also discussed,and Benzo?a?pyrene toxic equivalent factor?BaPeq?is used to assess the risk of cancer.The concentrations of toxic equivalents in spring,summer,autumn and winter were 1.78,0.09,3.38 and7.98 ng m^-3,respectively,which exceeded the EU standard limit(1 ng m^-3)except in summer,but not exceed the toxic equivalent concentration(10 ng m^-3).During the whole sampling period,the lifetime cancer risk?ECR?value is 3.00×10^-4,which exceeds the highest acceptable level(10^-610^-4),indicating that the exposure to air has a high risk of cancer,especially in the winter,ECR=6.9×10^-4.As and Cr in PM_2.5has been proved have carcinogenic risk to human health.Cd and Ni has no obvious carcinogenic risk to human body,non-carcinogenic health risk from high to low is Mn>Pb>Cr>Zn>Cu>As>Cd>Ni.PM_2.5 pollution was affected by the increase industrial economic growth due to energy consumption.The transmission of pollutants between cities in the sub-region will also increase the pollution in the Beijing.There is a significant positive correlation between energy consumption in Beijing,Tianjin and Hebei and concentration of PM_2.5 in Beijing?r=0.47,p<0.05?.