Development Of Online Analysis Method For Intermediate Volatile Organic Compounds

Intermediate volatile organic compounds?IVOCs?is important precursors of secondary organic aerosols?SOA?.The concentration and composition distribution characteristics of IVOCs in the atmosphere is observed efficiently and accurately.It is helpful to further explore the pollution process of PM_2.5 and O₃,and to provide important technical support for pollution prevention and control,formulation of air pollutant emission standards and related industry standards.However,some components in IVOCs are identified,such as n-Alkanes and PAHs,and the rest are classified as unresolved complex mixture?UCM?due to their difficulty in desorption and detection.At present,IVOCs is usually observed through offline collection and analysis techniques.However,the offline analysis technology has the disadvantages of low time resolution and long analysis time period,which makes the time effectiveness of IVOCs observations limited.This research is based on the technology of thermal desorption-gas chromatography/mass spectrometry?TD-GC/MS?on-line analysis of VOCs,and develops a high-sensitivity and high-resolution IVOCs on-line analysis method.It was first used to track the concentration of IVOCs in the atmosphere of Xuhui District,Shanghai,and preliminary analysis was performed on the sources of IVOCs and their correlation with conventional pollutants.The experimental research is mainly divided into two parts,and the conclusions are as follows:?1?The TD-GC/MS system is divided into three parts:GC/MS system,the cold trap system and the sampling system.The working parameters of the three systems are systematically studied and optimized.An online analysis method for IVOCs is established,and Validity was verified.The TD-GC/MS system is divided into three parts:GC/MS system,cold trap system and sampling system.The working parameters of the three systems are systematically studied and optimized.Finally,an online analysis method for IVOCs was established,and the effectiveness evaluation of the method was passed.The IVOCs online analysis system can efficiently collect and analyze n-Alkanes and PAHs in IVOCs.Optimize components that may have residues,and minimize the system residual of IVOCs.In addition,the problem of IVOCs depositing on the wall of the sampling channel and causing blockage was solved,improving the accuracy of the analysis results.This greatly improves the accuracy of the analysis results.Finally,the feasibility evaluation of the IVOCs online analysis system was performed:the analysis results have good reproducibility;the RSD is less than 20%?10 ng standard sample?;the detection limit of the method fully meets the current target organic matter requirements for detection of medium environmental concentration.?2?IVOCs online analysis system has been confirmed with high time resolution?1-3 h?.Follow-up observations of IVOCs in Xuhui District of Shanghai were performed continuously through the IVOCs online analysis system,with sampling in four periods for a total of three seasons.Analyze the composition and distribution of IVOCs,their concentration levels,and their seasonal and daily changes.In addition,the associations between n-Alkanes,PAHs and UCMs and their correlation with conventional pollutants(PM_2.5,O₃,SO₂,CO)were analyzed.The following conclusions were reached:UCM IVOCs are the main components of IVOCs,followed by n-Alkanes and PAHs;Among the collected IVOCs samples,the result is TIVOCautumn,2018>TIVOCwinter,2018>TIVOCautumn,Expo>TIVOCspring,2019.The obvious early peak characteristics are positive correlations in winter samples IVOCs;n-alkanes,PAHs and UCMs.The winter samples are the most obvious,indicating that the three samples are most likely from the same emission source.Overall,they were positively correlated with PM_2.5,NO₂,and CO,and negatively correlated with O₃.According to the analysis,it can be concluded that IVOCs may be strongly involved in photochemical reactions in the ambient atmosphere and are very important for the formation of PM_2.5.