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2011年夏季8月,在西安交通大学主楼顶(距离地面约100m)运用MOUDI采样器采集了5套不同粒径大气气溶胶样品.经TMS硅烷化后运用GC/MS定量分析了生物二次有机气溶胶(BSOA)异戊二烯氧化产物(2-甲基丁四醇,C5-烯三醇和2-甲基甘油酸)、单蒎烯类氧化产物(顺蒎酸,蒎酮酸,3-羟基戊二酸和3-甲基-1,2,3-丁三酸)以及倍半萜烯氧化产物(倍半萜烯酸)浓度.结果显示:西安城区大气BSOA中主要以异戊二烯类为主,其次是单萜烯和倍半萜烯类BSOA,其氧化所产生的生物二次有机碳(BSOC)浓度分别为0.39μgC·m^-3,0.13μgC·m^-3和0.10μgC·m^-3.粒径分布研究表明:BSOA主要富集在细颗粒物上.MBTCA/CPA特征比值表明:采样期间西安城区BSOA主要来自本地源.老化程度较低. “,”In this study, concentration and size distribution of biogenic secondary organic aerosols ( i. e. , isoprene, pinene and sesquiterpene photooxidation products) in the summertime atmosphere of Xi'an city, China was characterized using a GC/MS technique after a conversion to TMS derivatives. Our results showed that BSOA in Xi'an are dominated by isoprene oxidation products, which accounted for around 80% of the total quantified BSOA. Biogenic secondary organic carbon derived from isoprene, α-/β-pinene and sesquiterpene were 0.39μgC·m^-3, 0, 13μgC·m^-3, 0. 10μgC·m^-3, respectively. Size distributions of the nine determined compounds suggest that BSOA in the city are enriched in fine particles. Compared to that in other cities and mountain areas the relatively lower ratio of MBTCA/CPA ratio of Xi'an BSOA indicates that BSOA in the city are mostly derived from local sources and more fresh.