RESUMO
Organic acids in atmospheric particulate matter are widely involved in various physical and chemical reactions in the atmosphere and contribute greatly to the formation of secondary organic aerosols and haze pollutions. Thereforeï¼ the concentration distribution characteristicsï¼ sourcesï¼ and secondary formation of organic acids in particulate matter are of great significance for further investigation of organic aerosols and their secondary transformation. Fine particulate matter ï¼PM2.5ï¼ samples were collected in Zhengzhouï¼ and three types of organic acidsï¼ including dicarboxylic acidsï¼ fatty acidsï¼ and resin acidsï¼ were analyzed to explore their species distributionï¼ seasonal variationsï¼ source contributionï¼ and secondary generation. Malonic acid ï¼di-C3ï¼ and succinate acid ï¼di-C4ï¼ were the most abundant in the identified dicarboxylic acidsï¼ which showed obvious seasonal variations in the order of summer > autumn > winter > spring. Fatty acids had the highest concentration in winter and the lowest concentration in springï¼ showing obvious bimodal advantagesï¼ with the most abundant compounds being palmitic acid and stearic acid ï¼C18ï¼. Principal component analysis and multiple linear regression ï¼MLRï¼ were used to analyze the source of organic acids in PM2.5 in Zhengzhouï¼ the results showed that 35% of the organic acids came from combustion and traffic sourcesï¼ 24% from cooking sourcesï¼ 23% from secondary formationï¼ and 17% from natural sources. The ratios of the selected marker species ï¼i.e.ï¼ di-C3 / di-C4ï¼ F/Mï¼ and C18ï¼1 / C18ï¼ were used as tracers for the secondary formation of the organic aerosol and its aging process. The results showed that the photochemical reaction was intense in summerï¼ and the proportion of organic aerosol aging or secondary production was highï¼ whereas the photochemical reaction was weak in winterï¼ and the aging degree of organic aerosol was low. Correlation analysis and MLR were used in combination to quantify the relative contribution of gas-phase oxidation and liquid-phase oxidation to dicarboxylic acid formationï¼ and the results showed that gas-phase oxidation played a dominant role in the sampling period ï¼accounting for 58%ï¼ï¼ especially in summer ï¼61%ï¼.