| China has made world-renowned progress in controlling atmospheric particulate matter pollution in recent years,but as pollution remains at high level,it is imperative to continue to strengthen pollution control.It has been shown that a considerable amount of atmospheric particulate matter comes from secondary particulate matter generated by homogeneous and non-homogeneous oxidation,which aggravates particulate matter pollution and promotes the formation of haze.And atmospheric Criegee Intermediates(CIs)are amphiphilic radicals with strong oxidative properties enabling them to react with a variety of substances in the atmosphere,such as carboxylic acids,alcohols,organic amines,etc.The products can participate in the formation of secondary organic particulate matter,which makes an important contribution to particulate matter pollution,especially haze pollution in China,so identifying the secondary particulate matter formation mechanisms is of great practical importance for haze pollution control.There are a wide variety of multifunctional compounds in the atmosphere,such as Highly Oxygenated Organic Molecules(HOM),Amino Acids(AA),Organosulfates(OS),etc.These compounds with multifunctional groups have more reaction pathways with Criegee intermediates,and the reaction products are often accompanied by an increase in carbon chain length,making them easier to interact with other substances into the particle phase,thus promoting the growth of particles and the aggravation of particle pollution.At present,the knowledge and understanding of the reaction of Criegee intermediates with multifunctional compounds still need to be deepened.In this dissertation,Density Functional Theory(DFT),Born-Oppenheimer Molecular Dynamics(BOMD)and classical Molecular Dynamics(MD)are used to systematically investigate the gas-phase and gas-liquid interface reactions of Criegee intermediates with three typical multifunctional compounds in the atmosphere and the nucleation of the products at the molecular level.The main studies and conclusions are as follows:1.Gas-phase and gas-liquid interface reaction mechanism of Criegee intermediates with 2-methylglyceric acid2-Methylglyceric acid(MGA)is a highly oxygenated organic molecule produced by the oxidation of isoprene,which is widely present in the atmosphere,and is a typical class of secondary organic aerosol tracer with a relatively high concentration in the atmosphere.2-Methylglyceric acid contains one carboxyl group and two hydroxyl groups in the molecule,which is a typical multifunctional compound.This part of the study systematically explored the potential reaction pathways of two Criegee intermediates,CH2OO and CH3CHOO(anti-CH3CHOO,syn-CH3CHOO),with 2-methylglyceric acid in the gas phase,and simulated the reactions of CH3CHOO with 2-methylglyceric acid at the gas-liquid interface.The role of hydrogen bonds between the three functional groups of 2-methylglyceric acid in the reaction with CH3CHOO was investigated in the gas-phase reaction based on the strategy of hydrogen atom substitution of functional groups.The results showed that the reaction of the Criegee intermediate with the carboxyl group with 2-methylglyceric acid has the lowest energy barrier in the gas-phase reaction and is the main reaction pathway,and this reaction process is less influenced by the hydroxyl group.The reaction energy barrier of Criegee intermediate with the hydroxyl group of 2-methylglyceric acid is relatively high,and it is influenced by the carboxyl group and another hydroxyl group:the hydrogen bond between two hydroxyl groups and between the hydroxyl group and carboxyl group are not conducive to the reaction,and the more hydrogen bonds,the higher energy barrier.Water molecules can inhibit the reaction between the Criegee intermediate and the carboxyl group,but water molecule acts as a catalyst to promote the reaction between the Criegee intermediate and the hydroxyl group.In the gas-liquid interface reaction,the water molecules at the interface play the role of proton transfer,and 2-methylglyceric acid can also act as a medium of proton transfer to promote the hydration of Criegee intermediates.The specific process of product nucleation was obtained based on molecular dynamics simulation,which demonstrated the promotion of product nucleation by water molecules.In summary,this study elucidates the inhibitory effect of hydrogen bonding between functional groups on the oxidation reaction of Criegee intermediate with 2-methylglyceric acid,reveals and confirms that the reaction products of Criegee intermediate with 2-methylglyceric acid can promote the formation of new particles.2.Gas-phase and gas-liquid interface reaction mechanism of Criegee intermediates with serineAmino acids are important components of bioaerosols.Serine(Ser),one of the most abundant amino acids in the atmosphere,exists in a free or combined state and contains carboxyl,amino and hydroxyl functional groups in the molecule.In this study,the reaction mechanism of CH3CHOO with three functional groups of serine was investigated using the Density Functional Theory method.The highest reactivity of the carboxyl functional group,the second highest reactivity of the amino group and the lowest reactivity of the hydroxyl group of serine were obtained from the calculation.Meanwhile,the systematic analysis of the effect of water molecule on the reaction reveals that water molecule can inhibit the reaction of Criegee intermediates with carboxyl group and promote the reaction with amino and hydroxyl groups.Based on the Born-Oppenheimer molecular dynamics simulations,it was found that the reaction pathways of anti-CH3CHOO with three functional groups of serine at the gas-liquid interface were obviously different,the results showed that(1)only direct reaction pathway were observed in the reaction with carboxyl functional group;(2)for the amino group,there are direct and water-mediated reactions;(3)in the reaction with hydroxyl group,only water-mediated reaction pathway was observed.Further molecular dynamics simulations showed that the products of Criegee intermediates with serine,sulfuric acid,ammonia and water molecules can nucleate in atmospheric environments and water molecules can promote the growth of cluster.The above studies elucidate the reaction mechanism of Criegee intermediates with serine in the gas phase and at the gas-liquid interface,and confirm the contribution of the reaction products to new particle formation in the atmosphere.3.Gas-phase and gas-liquid interface reaction mechanism of Criegee intermediates with glycolic acid sulfateGlycolic acid sulfate(GAS)is a typical organonitrate in the atmosphere with atmospheric concentration up to 60 ng m-3.In this study,Density Functional Theory and Born-Oppcnheimer molecular dynamic were used to explore the reaction mechanism of Criegee intermediate with glycolic acid sulfate in the gas-phase and at the gas-liquid interface,respectively.The results obtained that both anti-CH3CHOO and syn-CH3CHOO can react with the carboxyl and organonitrate groups of glycolic acid sulfate in the gas-phase reaction with generally low energy barriers(1.00～4.09 kcal/mol).At the gas-liquid interface,direct and water-mediated reactions between anti-CH3CHOO and two functional groups were observed,and two functional groups can participate in the addition reaction of the Criegee intermediate at the same time,the interaction of the two functional groups leads to the intramolecular proton transfer during the reaction.In addition,glycolic acid sulfate can participate in the hydration reaction of the Criegee intermediate as a proton donor,and intramolecular proton transfer was also observed during the reaction.Nucleation simulations based on molecular dynamics show that the products containing sulfate groups in an aqueous environment are more likely to form larger diameter clusters,and the diameter of clusters formed in an aqueous environment is larger than that in an anhydrous environment.This study provides some insights into the reaction of glycolic acid sulfate functional groups with Criegee intermediates at the gas-liquid interface and the mechanism that glycolic acid sulfate promotes the hydration of Criegee intermediate,and reveals the influence of water molecules on the size of nucleated clusters.In summary,by systematically analyzing the reaction mechanism of Criegee intermediates with several types of typical multifunctional compounds in the atmosphere,the basic principle that the interaction between multifunctional groups of compounds in gas-phase reactions reduces the reactivity of Criegee intermediates was elucidated,and the promotion or inhibition mechanism by water molecule of different reactions were revealed;the reactivities of carboxyl,amino,hydroxyl,and sulfate groups with Criegee intermediates were calculated.In addition,this study reveals that a single functional group can react with Criegee intermediates independently in gas-liquid interface reaction,and multifunctional groups can also react with Criegee intermediates simultaneously through an intramolecular proton transfer mechanism.The results indicated that the reaction products of Criegee intermediates with multifunctional compounds can promote the formation of atmospheric particles.This study provides data support for the accurate assessment of the sources of atmospheric secondary particulate matter and provides theoretical support for the control and management of the atmospheric particulate matter. |
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