| As the second largest economy in the world,China has developed rapidly.While economic growth is accompanied by serious environmental problems,The ozone pollution in China has attracted much attention in recent years.Ozone precursors,especially volatile organic compounds?VOCs?,are extremely important for the generation of ozone.Taiyuan is one of the cities that heavily affected by the coking in the country.There are no reports on the regional pollution characteristics of VOCs in Taiyuan.In this study,the GC-FID/MSD system was used to analyze 66 VOCs in ambient samples at four sites of Taiyuan in summer,autumn,and winter in 2019.The characteristics and spatial-temporal distribution of VOCs were analyzed based on conventional atmospheric pollutants and meteorological data.And using the propylene-equivalent,the maximum increment reactivity?MIR?method and the aerosol generation coefficient?FAC?to calculate the production potentials of VOCs to tropospheric ozone and secondary organic aerosol?SOA?to study the photochemical reaction of ambient VOCs.In addition,identify the sources and potential source areas of ambient VOCs at different sites in Taiyuan with the help of ratio analysis,Positive matrix factorization model?PMF?,and CWT.At last,the lifetime cancer risk?LCR?and hazard ratio?HR?of VOCs were used to evaluate the carcinogenic risk and non-carcinogenic risk from the inhalation exposure of VOCs,respectively.The main conclusions were as follows:?1?The average concentration of VOCs in 122 valid samples measured in Taiyuan in summer and autumn of 2019 was 36.82 ppbv,in which alkane was the main component and accounted for 48.80%.Besides,affected by local emissions,meteorological conditions,and transport,the atmospheric VOCs concentration in Taiyuan shows a trend of winter?50.08 ppbv?>autumn?39.94 ppbv?>summer?20.44 ppbv?,and the contribution of aromatic and alkanes increased significantly in autumn and winter.?2?From a spatial point of view,the concentration of VOCs?43.58 ppbv?at Xiaodian site is the highest,which is because the site is located in a residential mixed traffic area,and affected by the nearby resident emission sources and traffic sources.Low-carbon compounds and benzene are the most abundant species of VOCs at various points.Besides,there are differences in the main VOCs species at each sampling site in Taiyuan.The isoprene concentration at the Shanglan site sampling point occupies an important position in summer;the concentration of isopentane and n-pentane at the Taoyuan site are higher than that at other sites.?3?Coking sources and combustion emission were identified as the main pollution sources of the atmospheric VOCs in Taiyuan by using ration analysis and PMF model,accounting for 30.59%and 24.96%respectively.Followed by vehicle emissions?24.05%?,solvent use?15.57%?,and plant emissions?9.82%?.The CWT results indicate that the Taiyuan Basin?such as Qingxu?and the northern Linfen Basin are potential sources areas of VOCs in Taiyuan.?4?Alkenes are the most photochemically reactive VOCs component in Taiyuan,and their contributions to propylene-equivalent concentrations and ozone formation potentials?OFP?all showed a trend that is greater in autumn than in summer.The range of SOA formation potential estimated by the FAC method is 0.21-1.64?g/m3.Aromatic is the largest contributors,accounting for 91.22%.And BTEX?benzene,toluene,ethylbenzene,m,p-xylene and o-xylene?is the most important species.Combined with the source,in order to realize the prevention and control of O3 and SOA,corporate supervision such as coking,combustion and solvent use should be paid more attention.?5?The lifetime cancer risk?LCR?value of benzene in Taiyuan City exceeded the carcinogenic risk value(1×10-6)acceptable by adults both in summer,autumn,and winter.The non-carcinogenic risk assessment results showed that although the average HR value of each VOCs at all site was less than 1,some samples of benzene had an HR value greater than 1,especially in winter.There is still an actual risk of chronic disease.Attention should be paid to the prevention and control of benzene to prevent the possibility of increasing non-carcinogenic risk.The prevention and control of benzene in Taiyuan should be paid attention to,strengthening the supervision of coking and combustion emissions to decrease the possibility of increasing human health risks.This work describes the level and regional characteristics of VOCs in Taiyuan,clarifies the main sources and risks substances of VOCs,and enriches the VOCs database of cities affected by coking,which provides a scientific basis for government to prevention and control in group of VOCs in Taiyuan. |
PDF Full Text Request