The Mechanism Of Homogeneous Reaction And Heterogeneous Nucleation In VOCs Degradation Process In The Atmosphere

Volatile organic compounds(VOCs)pollutants and persistent organic pollutants(POPs)play an important role in the process of atmospheric chemical reactions.At present,through the experimental and theoretical calculation methods,their degradation process in the atmospheric environment has been studied extensively.Trichloroethylene is a typical volatile organic pollutants and persistent organic pollutants,and it is widely used in industrial production and commercial activities as a kind of chlorinated unsaturated alkene.When it is discharged into the atmosphere and the surface of the water,the atmospheric environment and water environment caused serious pollution,which seriously harm to human health.Biomass combustion is an important source of atmospheric particulate pollutants,and it has an important influence on air quality,trace gas emission,carbon cycle and ecosystem structure and function in the atmosphere.Volatile organic compounds(VOCs)are one of the main products of biomass combustion,which plays an important role in the formation of two organic aerosol in atmosphere.Levoglucosan and sucrose are typical molecular tracers of volatile emission from biomass combustion,and they are the main water-soluble organic matter in haze,which is a good tracer of biomass combustion sources.In this paper,we use quantum chemistry theory,through density functional method(DFT).The reaction mechanism of trichloroethylene,levoglucosan and sucrose with free radicals in atmosphere are studied at MPWB1K/6-311-G(3df,2p)//MPWB1K/6-31+G(d,p)level.The transition state theory(TST)is used to calculate the kinetic data of the main elementary reactions,and the GROMACS 4.5.5 package with Amber99SB force field was used for all molecular dynamics simulations of the mechanism of heterogeneous nucleation of CI free radicals produced in the process of TCE ozonation.The results are as follows:1.Study on the degradation reaction of TCE by O3 and some main free radicals in the atmosphere and the mechanism and kinetics of the subsequent reactionIn the ozonation of TCE,two kinds of Criegee radical are generated,and they can react with NO,NO2,SO2,H2O,O2 and other species in the atmosphere.Active species,such as OH radical,Cl radical,O3 and other new radicals can also be produced and then will improve the oxidation ability of atmosphere.In the oxidation process,the NO3 be formed eventually through Criegee radical react with NO and NO2,and SO2 can also be oxidized to SO3,which can easily produce inorganic acid in atmosphere.Inorganic salts(NH4)2SO4 and NH4NO3 can be generated in the presence of NH3.Furthermore,theoxygen-containing heterocyclic intermediates,organic nitrogen,organic sulfur compounds,and hydroxy compounds can be obtained too.These species may contribute to the formation of fine particles and SOA.The rate constants for TCE initiated by NO3,OH radical,HO2 radical,SO4-radical,Cl radical,O3 in atmosphere at 298.15K is relatively smaller for KTotal(9.59×10-15cm3molecule-1s-1),however,slow degradation will persistent affect the atmosphere environment.Furthermore,high concentration area can accelerate the rate of initial reaction.2.Study on the mechanism of heterogeneous nucleation of Cl free radicals produced in the progress of TCE ozonationIn the process of TCE ozone oxidation,the primary ozonation POZ is formed,POZ has two open loop decomposition path,and two chloro-CI radicals were produced,respectively.The effect of atmospheric temperature on the heterogeneous nucleation process of fine particles was studied by molecular dynamics simulation.The results show that in Organic Compounds-(NH4)2SO4-H2O system,the degradation reaction induced by O3 in TCE and its subsequent reaction,the inorganic salts,organic nitrogen and organic sulfur compounds,oxygen heterocyclic intermediates and polyhydroxy compounds can be obvious spontaneous nucleation,and a new fine particle with a diameter of about 2nm was formed.It provides a good research model for the formation of volatile organic compounds from the atmosphere.3.Oxidative degradation mechanism of levoglucosan and sucrose in atmosphereIt has been reported that the mechanism of gas phase reaction of OH radical and levoglucosan in atmosphere,but as a kind of water soluble carbohydrate,liquid phase reaction occurs in the atmosphere aerosol.Therefore,we investigated the mechanism of the liquid phase reaction between OH radical and levoglucosan in the atmosphere.The study shows that the liquid phase,OH radical can trigger the extraction-H reaction of levoglucosan.In addition,the extraction-H reaction of SO4-radicals and NO3 with in levoglucosan in the gas phase was studied.The results show that the H-atoms of levoglucosan can be extracted by SO4-radicals and NO3.The mechanism of the oxidative degradation of the free radicals in the atmosphere was further studied.In addition,the mechanism of oxidative degradation of OH free radical and sucrose was studied.Sucrose as a two sugar,is similar to the hydrogen extraction reaction of OH radical with levoglucosan,sucrose can also react with OH radicals by hydrogen extraction.The reaction mechanism of O2,NO and H2O in the atmospheric environment was studied.The results show that the OH radical can initiate the hydrogen abstraction reaction of sucrose,and the final products has some contribution to the formation of atmospheric acidity and SOA.