Optimization And Application Of Comprehensive Iwo-Dimensional Gas Chromatography Analysis Method For Semi-/Intermediate Volatile Organic Compounds In The Atmosphere

Fine particulate matter(PM_2.5)has a strong impact on regional air quality,climate change and human health.Secondary organic aerosol（SOA）accounts for significant fractions in fine particles.Semi-/Intermediate-volatile organic compounds（S/IVOCs）play an important role in ambient air.As important precursors of SOA,they are considered to be important components that can make up the difference between the model simulated and actual observed values of SOA.Understanding the source,composition,concentration level and chemical reaction process of S/IVOCs will help to get better and further explore and improve the generation mechanism of SOA.Understanding the mechanism and characteristics of S/IVOCs to generate SOA can help to evaluate the impact of S/IVOCs on environment accurately,and provide a research foundation for effective control of regional composite pollution in China.Semi-/Intermediate-volatile organic compounds are organic compounds with saturated vapor pressure between 10^-1～10⁵μg/m³,which can exist in both gas and particle phases at the same time,and can generate lower volatile organic compounds through reaction.In the current research,S/IVOCs mainly include C₁₀～C₃₀ straight chain alkanes,C₁₅～C₂₇ cycloalkanes,C₁₈～C₂₀ branched alkanes,C₁₀～C₂₄ aromatic hydrocarbons and a small amount of ketones,aldehydes and acids.S/IVOCs come from a wide range of sources,which can be directly discharged into natural and man-made sources,and can also be generated by the reaction of VOCs with oxidants（O₃,OH and NO₃）in ambient air.In recent years,regional composite pollution has become a major environmental problem in the eastern coastal areas and large cities,especially in the Pearl River Delta,Yangtze River Delta and Beijing-Tianjin-Hebei region.These super-large urban clusters are the main anthropogenic emission areas,and pollution problems such as SOA and PM_2.5 are prominent.Therefore,to further explore the sources and composition of S/IVOCs in the atmosphere,to carry out the measurement of S/IVOCs and their key intermediate components in the ambient air,and to obtain the information about the components and sources of S/IVOCs will help to optimize the existing SOA generation mechanism and modify the yield parameters of SOA generation.It is helpful to further control and treat the problem of atmospheric pollution.In this study,a comprehensive two-dimensional gas chromatography method combined with field observations and laboratory processing was used to measure S/IVOCs in the ambient air in the Pearl River Delta from September to November 2019.The measurement results were compared with the measurement data results of the PTR-To F-MS methods sampled and analyzed in the same period,and the correlation analysis was carried out in combination with the measurement data of related meteorological parameters.Comprehensive two-dimensional gas chromatography has a wide range of applications,suitable for the analysis of more complex samples,and is currently widely used in the analysis of petrochemical,perfume,flavor and environmental samples.Compared with traditional one-dimensional gas chromatography,comprehensive two-dimensional gas chromatography solves the problem of chromatographic peak overlap,has higher sensitivity,and can effectively separate complex components.During the observation period of ambient air in the Pearl River Delta,the research results of S/IVOCs showed that the average particle phase concentration of n-alkanes was 1～14.7 ng/m³,and the PAHs were 0.1～4.08 ng/m³;The average gas phase concentration of n-alkanes is 2.3～169.5 ng/m³,and PAHs is 0.2～33.9 ng/m³..The concentration of n-alkanes is generally higher than that of polycyclic aromatic hydrocarbons in both gas phase and particle phase.In the gas phase,the total concentration of n-alkanes is about 4.5～81 times that of polycyclic aromatic hydrocarbons,with an average of 20 times;in the particle phase,the total concentration of n-alkanes is about 0.5～123 times that of polycyclic aromatic hydrocarbons,with an average of 13 times.When analyzing the gas-particle distribution characteristics of the target,it is found that the target concentration in the gas phase is significantly higher than that in the particle phase,up to 16 times.With the increase of carbon number,the proportion of compounds in the particle phase increases.The influence of temperature and pressure on gas particle distribution is more obvious in the Pearl River Delta observation.When the ambient pressure increases or the temperature decreases,the particle phase concentration will increase.