Mechanism And Kinetics Of Ozonolysis Of Syringaldehyde And ?-myrcene

The main sources of Volatile Organic Compounds?VOCs?in the atmosphere are the natural and anthropogenic emissions.The emission of biomass combustion in China accounts for 23.3%of the total anthropogenic VOCs emissions,and a series of lignin pyrolysis products-methoxy phenols are produced during the combustion process.However,natural source of VOCs emissions dominate the global VOCs emissions,mainly consisting of isoprene and the monoterpene compounds.VOCs,once discharged into the atmosphere,can directly affect human health,and can react with oxidants in the atmosphere,such as OH,NO₃and O₃ to produce chemical compounds of higher oxidation state,and increase the organic composition of atmospheric particles and form secondary organic aerosols?SOAs?.The secondary organic aerosol is the main factor which causes the decrease of visibility and the haze weather.In the process of the reaction,the regional ozone concentration will be exceeded and the air quality is affected.Most of the methoxyphenolic compounds have low volatility and can easily adsorb on the surface of the particles,subject to possible heterogeneous degradation with the oxidants in the atmosphere.Myrcene is one of the monterpene emitted by plants.The structure contains multiple double bonds and has high reactivity.The oxidation products of myrcene in the atmosphere contribute greatly to SOAs.The heterogeneous reaction of ozonolysis of syringaldehyde on the surface of particles and the gas-phase ozonolysis of myrcene were studied in this thesis.1?I have constructed a system to study the degradation syringaldehyde on surfaces.Thesystem is consisted of an ozone generator,a reaction device reformed by a rotaryevaporator,a constant temperature water bath and an ozone analyzer.HPLC was usedto quantify the syringaldehyde on the surface of particles on different time points,andthe reaction time was plotted to get pseudo first order kinetic rate of syringaldehyde.Two different heterogeneous dynamic models were used to fit the pseudo first orderrate constant and the concentration of ozone to obtain the secondary order ozonolysisrate constant and the adsorption equilibrium constant of ozone on the surface of theparticles.The secondary order ozonolysis reaction rate constants of syringaldehyde inkaolin and SiO₂ surface are 4.10×10^-17 and 8.08×10^-1818 cm³ molecules^-1 s^-1 respectivelyby the pseudo cooperative graph of the heterogeneous reaction kinetic model.Based onthis calculation,the atmospheric lifetime of syringaldehyde is 4.8-9.86 h when theozone concentration is 7×10¹¹ molecules cm^-3.2?The reaction mechanism of ozonlysis of myrcene was simulated by high level quantumchemistry and kinetic theory calculation.It is found that O₃ will be added to the mono-double bonds of myrcene to form primary ozonides?POZs?,and POZs will rapidlydecompose to form 4-Vinyl-4-Pentenal+?CH₃?₂OO,syn-My-CI+?CH₃?₂CO and anti-My-CI+?CH₃?₂CO,and the branch ratio of the three primary product channels is 0.73,0.04,0.23,respectively.The high excited state Criegee intermediates?CIs?can berapidly isomerization or be thermalized to stabilized CIs?sCIs?.The branch ratios of?CH₃?₂OO*,syn-My-CI*,and anti-My-CI*are 0.60,0.23,0.25,respectively.Syn-My-sCI,anti-My-sCI can undergo unimolecular H-migrationto form a vinyl hydroperoxide.The vinyl hydroperoxide can rapidly decompose to OH and a vinoxy-type radical.Anti-My-CI would most likely react with water vapor or cyclize to a bicyclic compoundwhen relative humidity is low.Through the comparison of reaction rate,only under thecondition of low humidity at low temperature?<273K?,the bimolecular reactionbetween My-CIs and SO₂ is the main path.