| Volatile organic compounds(VOCs)have the characteristics of toxicity and photochemical reactivity,and are the main organic pollutants in urban air.According to the pollution characteristics and source characteristics of VOCs,it is of great significance to carry out research on the analysis of VOCs sources and accurately identify the sources and contribution degrees of VOCs in ambient air,which is of great significance for subsequent air pollution prevention and control.Taking the spatiotemporal distribution and change law of VOCs in typical urban air as the main line,this paper carries out relevant research through the theoretical and advanced technical means of environmental chemistry and organic pollution chemistry,combined with a large number of mathematical model calculations,takes the urban areas of Fuzhou and Beijing as the research area,collects ambient air samples in the two urban areas,comprehensively studies the species categories and pollution characteristics of air VOCs,reveals the temporal and spatial variation law of VOCs,and analyzes the sources of VOCs in the air of different cities.To explore chemical reactivity and its contribution mechanism to ozone formation,and to assess the potential health risks of VOCs.The main results achieved are as follows:(1)The concentration level and distribution characteristics of major volatile organic compounds such as alkanes,olefins and aromatic hydrocarbons in the air in the study area were clarified.Overall,the average concentration of VOCs in urban areas of Fuzhou was 10.733ppbv,with alkanes contributing 60.3%,aromatic hydrocarbons accounting for 32.3%,and olefins accounting for 7.4%.The average concentration in urban area of Beijing was 21.241ppbv,with alkanes contributing 63.72%,olefins accounting for 20.54%,and aromatic hydrocarbons accounting for 15.74%.The spatial distribution differences and temporal variation of VOCs in the study area were revealed,and the spatial variation law of concentration was as follows:The concentration of ambient air TVOC in urban area of Fuzhou City showed bimodal changes,and the concentration of ambient air TVOC in urban area of Beijing showed unimodal change.(2)The ozone formation potential(OFP)value of VOCs in the study area was clarified,and the formation value of secondary organic aerosol(SOA)was estimated by using the aerosol generation coefficient.The OFP of VOCs in urban areas of Fuzhou was 30.23ppbv,and the OFP contribution rates of aromatic hydrocarbons,olefins and alkanes were 48.23%,26.05%and 25.72%,respectively.The OFP of VOCs in urban areas of Beijing was 68.812 ppbv,and olefins contributed the most to OFP,with 57.32%,followed by aromatic hydrocarbons and alkanes,with 23.57%and 19.11%,respectively.Aromatic hydrocarbons play an absolute role in the contribution to SOA generation.(3)The principal component analysis method was used to analyze the source of VOCs in the air in the study area,and it was concluded that motor vehicle exhaust was the most important source in the two urban areas.The positive definite matrix factor decomposition(PMF)model was used to analyze the source of VOCs in the air of the two urban areas,and it was concluded that motor vehicle exhaust was the most important source in the two cities,accounting for 55.07%and 41.15%respectively.The PMF model has more advantages in the analysis of VOCs pollution sources,but through the comparative analysis of the two models,the source analysis results can be more convincing.(4)The risk assessment of VOCs in the air in the study area was carried out,and it was found that for the non-carcinogenic risk,the non-carcinogenic risk hazard quotient values of VOCs in the air in the two urban areas were within the safe value recognized by the US EPA,while the carcinogenic risk values such as benzene exceeded the limit value,and it was recommended to take active countermeasures to effectively reduce the impact on the health of residents. |
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