| With the rapid development of China’s economy,air pollution is increasingly serious.Moreover,air pollution is also developing towards a variety of sources and pollutants.Atmospheric aerosol can not only affect climate and air quality,but also harm human health.Therefore,it has become an urgent problem restricting economic and social development.There are many organic species in the atmosphere,and the nucleation of organic matter has become a hot topic in recent years.Among them,organic amines and organic acids have been proved to play an important role in nucleation.Aromatic acid is a kind of common organic acid in the atmosphere,and studies have proved that the existence of a small amount of aromatic acid can promote the nucleation of sulfuric acid-water system.Because acids tend to condense more easily in the presence of bases,the presence of ammonia and organic amines can speed up nucleation and growth of new particles.The nucleation mechanism of aromatic acids and organic amines is very complex.Therefore,it is very important to explore the microscopic nucleation mechanism of common atmospheric nucleation precursors such as aromatic acid and sulfuric acid,ammonia and organic amine by means of quantum chemistry calculation.Moreover,ammonia and organic amines in the atmosphere can not only participate in the new particle formation,but also can catalyze chemical reactions in the atmosphere(hydrolysis reaction,isomerization reaction,monomolecular reaction and rearrangement reaction)to increase or decrease the reaction barrier.In atmospheric chemistry,ammonia and organic amines can have a series of chemical reactions with photooxidants,volatile organic pollutants,nitrogen oxides,and sulfides in the atmosphere.The reaction products can further nucleate and form molecular clusters,which then grow into observable fine particles through condensation and collision,resulting in the formation of aerosols and secondary pollutants.Therefore,the study of ammonia and organic amines involved in nucleation and some atmospheric reaction process can provide a theoretical basis for governance and environmental legislation.Therefore,by means of quantum chemistry calculation,the nucleation of several typical aromatic acids and some common nucleation precursors(water,sulfuric acid,ammonia,monomethylamine,dimethylamine,trimethylamine)in the atmosphere was studied.The effects of hydration and different relative humidity conditions on nucleation of aromatic acid with sulfuric acid,ammonia and dimethylamine were studied.The hydrolysis of ketene to acetic acid catalyzed by ammonia and organic amine was also studied.The research content includes the following three parts.1.Theoretical Study on the Interaction of Aromatic Acid with Common Nucleation Precursors in AtmosphereAromatic acid is a kind of common organic acid in the atmosphere,which comes from a wide range of sources.Moreover,aromatic acid can participate in the new particle formation and have an impact on atmospheric aerosols.The interaction between several typical aromatic acids and some common nucleation precursors in the atmosphere was studied by using density functional theory(DFT)at the PW91PW91/6-311++G(3df,3pd)level.The research content is the interaction of benzoic acid(BA),phenylacetic acid(PAA),phthalic acid(PA),isophthalic acid(mPA),and terephthalic acid(PTA)with sulfuric acid(SA),water(H2O),ammonia(NH3),methylamine(MA),dimethylamine(DMA),and trimethylamine(TMA).The study showed that the BA/PAA/mPA/PTA-SA complexes have the lowest Gibbs free energy,followed by the BA/PAA/mPA/PTA-DMA complexes.For the clusters containing PA,the two carboxyl groups in the ortho-position that formed an intra-molecular hydrogen bond promoted the interaction of NH3 and amines,but hindered the interaction of SA.For a given aromatic acid,when the two carboxyl groups were in the meta-position and para-position,the extra carboxyl had little influence on the complexation.The presence of aromatic acid has a significant effect on the stability of sulfuric acid,and it can lower the evaporation rate of clusters.However,the presence of aromatic acid alone is not conducive to new particle formation.The atomatic acid-H20 clusters have the highest concentrations in the formation of heterodimers.Simultaneously,although the concentrations of aromatic acid-SA/NH3/amine clusters are relatively a little low,they also have the potential to form during the formation of heterodimers owing to the relative low Gibbs free energies.2.Effects of Hydration on Nucleation of Benzoic Acid-Sulfuric Acid/Ammonia/DimethylamineThe atmospheric water content is abundant,and water plays an important role in the atmospheric nucleation.In order to study the effect of hydration on the nucleation of BA-SA/NH3/DMA,the density functional theory(DFT)was used to study the effect of 0-6 water molecules on the nucleation of BA-SA/NH3/DMA at PW91PW91/6-311++G(3df,3pd)level.The influence of different humidity on nucleation of BA-SA/NH3/DMA and its atmospheric implication were also studied The results showed that when the BA is unhydrated and NH3 is hydrated with two water molecules,the cluster has the lowest Gibbs free energy.The interaction between BA and DMA is similar to the interaction between NH3 and BA,the cluster has the lowest Gibbs free energy value in presence of two water molecules.The result shows that hydration did not promote the formation of BA-NH3/DMA clusters.For the BA-SA hydrated clusters,when benzoic acid is hydrated with six water molecules and sulfuric acid is unhydrated,the cluster has the lowest Gibbs free energy.In general,increasing the degree of hydration promotes the interaction between benzoic acid and sulfuric acid.The result also reveals that hydrate distribution of the clusters is not sensitive to the different RH levels,and dry clusters accounts for the majority in different RH.The concentration of BA-SA cluster can reach the same order of magnitude as that of the(SA)2,particularly under polluted areas with the high concentration of BA.3.Theoretical Study on the Mechanism of Hydrolysis of Ketone into Acetic Acid Catalyzing by Ammonia and Organic AminesAmmonia and organic amines are not only abundant in content,but also can play a role in promoting many atmospheric reactions.In this chapter,the hydrolysis of ketone to form acetic acid catalyzed by ammonia and organic amines were studied by using the method of quantum chemical calculation at M06-2X/6-311+G(3df,2p)//M06-2X/cc-pVTZ level.The results show that it is difficult for ketene to be hydrolyzed into acetic acid or ene-diol complex under atmospheric conditions,so there may be a catalyst to reduce the reaction barrier and promote the reaction.The results showed that adding catalysts(water,ammonia,or organic amines)can effectively reduce the reaction barrier and make the reaction more likely to occur.The general trend for the formation of either acetic acid or ene-diol is that the catalytic effect of organic amines is better than that of ammonia,and the catalytic effect increases as more hydrogen atoms are replaced by methyl groups.At the same time,with the enhancement of catalysis,the possibility of direct hydrolysis of ketone into acetic acid increased,and the possibility of hydrolysis to ene-diol decreased gradually.When catalyzing the hydrolysis of ketene and the tautomerization of ene-diol complex,ammonia or organic amine has a synergistic effect with water.In other words,the coexistence of ammonia/organic amine and water can further lower the potential barrier. |
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