| Atmospheric peroxy radical chemistry is an important part of tropospheric atmospheric chemistry,which is of great significance for understanding the core scientific problems such as atmospheric oxidation,photochemical ozone and secondary organic aerosol generation.Organic peroxy radicals(RO2),a key intermediate in tropospheric chemistry,have a controlling influence on atmospheric radical cycling and the production of secondary pollutants such as ozone and secondary organic aerosols(SOA).In remote areas,i.e.under clean atmospheric conditions,organic peroxy radicals mainly undergo self-reactions,cross-reactions with HO2 radicals or other RˊO2 radicals,which are the main sinks for RO2 under these conditions.Self-reactions and cross-reactions of peroxyl radicals have a significant impact on the concentration of tropospheric HOx(OH,HO2)species.RO2 self-reactions not only lead to a decrease in local ozone production because some of the self-reaction products are stable substances,this also leads to a decrease in the concentration of free radical species in the atmosphere and therefore self-reactions are also important for the fate of RO2 in the atmosphere.In this thesis,the kinetics of the self-reaction of ethyl peroxyl radical,butyl peroxyl radical and cyclopentyl peroxyl radical were investigated by using advanced vacuum ultraviolet photoionization mass spectrometry(VUV-TOF-MS)in the laboratory using a microwave discharge flow tube as a reactor.The photoionization mass spectra were obtained using a vacuum UV discharge lamp with 9.6 eV and 10.6 eV photon energy as the photoionisation source,respectively,from which the products in each channel of the autoreaction could be observed.At the same time,kinetic experiments were carried out by varying the reaction time in order to confirm the origin of the products and to verify the reaction mechanism.Based on the fitting of the kinetic data to the theoretical calculations and the comparison of the peak areas in the photoionization efficiency spectra,the channel branching ratios of the dimer product ROOR were predicted.The specific research in this thesis has three main components:1.The study on self-reaction of ethyl peroxy radical C2H5O2.The products of C2H5O2 self-reaction ethoxy C2H5O,acetaldehyde C2H4O,ethanol C2H5OH and the dimer C2H5OOC2H5 were observed using VUV-TOF-MS,followed by kinetic experiments and simulations to confirm the origin and mechanism of the self-reaction products.Based on the fitting of the peak area ratios of the photoionization mass spectra and the kinetic results,we suggest that for the dimer product C2H5OOC2H5 channel with a branching ratio of approximately 10±5%.The potential energy surface of the C2H5O2 self-reaction was also calculated and confirmed from theoretical calculations.2.The study on self-reaction of the butyl peroxyl radical C4H9O2.There are two isomers of C4H9O2,which will undergo self-reaction and cross-reaction in the flow tube reactor to produce butoxy C4H9O,butyric aldehyde C4H8O,2-butanone C4H8O and nbutanol C4H9OH and secondary butanol C4H9OH,and dimer butyl peroxide C4H9OOC4H9.We have also carried out kinetic experiments and simulations to confirm the origin and formation mechanism of some of the products Based on the peak area ratio of the photoionization mass spectra and the fitting of the kinetic results,we suggest a branching ratio of about 12±2%for the dimeric product C4H9OOC4H9 channel.3.The study on self-reaction of cyclopentyl peroxy radical C5H9O2.Cyclopentane can be used as the prototype hydrocarbon for the oxidation of cyclopentane.C5H9O2 undergoes self-reaction to produce cyclopentyloxy C5H9O,cyclopentanone C5H8O and cyclopentanol C5H9OH and the dimer cyclopentyl peroxide C5H9OOC5H9.Cyclopentyloxy can easily undergo "β-cleavage" and then ring opening at room temperature,resulting in new alkyl peroxy radicals involved in self-reactions or crossreactions with C5H9O2 to produce products such as glutaraldehyde.We also carried out kinetic studies to confirm the origin and formation mechanism of some of the above products by measuring the variation of mass spectral signals of key species with reaction time and kinetic theoretical simulations.Based on the fitting of the peak area ratio of the photoionization mass spectra and the kinetic results,we suggest a branching ratio of about 5%for the dimer product C5H9OOC5H9 channel and summarize a more complete mechanism of C5H9O2 self-reaction. |
