Distribution Characteristics And Source Apportionment Of The Organic Acids In Atmospheric Particulates

As one of the most important organic components in the atmospheric particulates,organic acids have a strong hygroscopicity which could affect global climate,atmospheric visibility and human health by changing size distributions of the particles and cloud condensation.Dicarboxylic acids(DCAs),as a big segment of the secondary organic aerosols(SOAs),are mainly formed by the multiple oxidative degradations of volatile organic compounds(VOCs).Concentration distributions of the organic acids vary from different sources and forming ways,and the formation mechanism and source of SOA are far from clear until now,the big gap between the smoke chamber and simulation with the observed results has been challenged,so it is of graet significance to make the actual composition and distribution of DCAs in the atmospheric environment for explaination of haze.Analysis focused on organic acids has been conducted with atmospheric particles from Xi'an in this work,and the main contents are as follows:The environmental effects,characteristic distributions,determination method,formation paths and source apportionment of organic acids in the atmospheric particulate matters were discussed systematically in the review section.The significance and main contents of this thesis were presented based on the most recent research and evolution of SOA in the atmospheric environment.Pollution characteristics of DCAs in particulate matters.PM2.5 and PM10 were sampled from three sites(urban,suburban and rural)in peried of July 13-July 24,2015 and Jan 8-Jan 28,2016.The gaseous organic acids were collected synchronously with absorption solutions.DCAs were extracted by polar solvents and then derivatived.A quantitative GC analysis method including 15 kinds of DCAs butyls has been set up.The detection limit 36.4-82.5 ?g/L and the precision and recovery of this method were both up to the analysis standard.The concentration distributions of DCAs in different regions,seasons,particle sizes and weather conditions were studied.The results show that DCAs content was higher in winter than in summer,and higher in haze days than in sunny days.The spatial distributions of DCAs in U were higher than in suburbs and villages,which indicates that urban DCAs pollutions were more serious than the suburban and rural.Concentration of the DCAs in PM2.5 was higher than in PM10,it revealed that DCAs compounds were more easily deposited in fine particle phase.Pollution characteristics of MCAs in particulate matters.MCAs were extracted with weak polar solvent,and then methyl esterified.32 kinds of methyl esters were quantitatively analyzed by gas chromatography.RSD value(less than 12%),recovery(69.2%?117.6%)and the detection limit(23.6-55.8 ?g/L)of this method can meet the quantitative analysis of MCAs in particulate matter samples.Molecular,seasonal,dimensional distributions of MCAs have been observed,Results showed that C16 is the highest content of MCAs,and a direct relationship between the concentration distributions and primary emissions was existed obviously.MCAs concentration in PM10 was higher than that of PM2.5 and the higher ratio of gas to particle distributions,which were the significant differentiation between DCAs and MCAs.Combined with the concentration distributions of organic pollutants and atmospheric oxidability,method of characteristic ratios and correlation analysis were applied to confirm the photochemical mechanism of DCAs in organic aerosols.Conclusions could be made that the DCAs were the products of secondary photochemical reactions in Xi'an and mainly affected by the concentration of photochemical oxidants,light intensity and other conditions.Another novel liquid-phase oxidation also should be an important path to DCAs,the relative humidity was the key to restrict the oxidation reaction.These mechanisms palyed a pivotal role for understanding the formation of the SOA evolution process were of great significance.