城市大气颗粒物表面半醌自由基的测定及特征分析

Measurements and characteristics of semiquinone radicals in urban atmospheric particles

采集上海市城区和郊区两个典型站位的大气颗粒物样品,通过二氯甲烷萃取分离并利用电子自旋共振波谱技术(ESR)分析测定吸附在颗粒物表面的稳定自由基.结果显示,测试样品的波谱特征表现为显著的三重信号峰,且g因子值均在2.00379—2.00395范围内,通过与醌类标准物质图谱比对,可以判断颗粒物表面至少吸附1种邻位半醌自由基.对自由基分布特征研究发现,自由基浓度的时空变化和粒径分布特征显著:闵行采样点的半醌自由基浓度远高于普陀采样点;在季节变化上表现为夏秋季半醌自由基浓度低于冬春季,其中春季最高,夏季最低;半醌自由基在不同粒径颗粒上的分布,呈现PM2.5>PM10>TSP的变化规律,说明自由基更容易富集在细颗粒上.

In the present study, atmospheric suspended particles from two representative sites of Shanghai were collected for the measurements of stable free radicals on the particle surface. Particle samples were extracted with dichloromethane and analyzed by electron spin resonance （ESR）. ESR spectra showed a triple peak signal with g-values of 2. 00379--2. 00395, consistent with the presence of ortho-position semiquinone radicals. The concentration of semiquinone radicals on the particles exhibited major spatial and seasonal variation in both sites. The concentration of semiquinone radicals in particles from Minhang was higher that from Putuo. The results also indicated that the concentration of semiquinone radicals in the summer and autumn was lower than that in the winter and spring. Furthermore, the order of the concentration of semiquinone radicals on different sized particle was TSP 〈 PM10 〈 PM2.5, indicating that semiquinone radicals could be more easily enriched in fine particles.