金属与水溶性有机物模拟大气颗粒物自由基生成的研究
Experimental simulation study of free radicals generated by water-soluble organic matter and metal-loaded particles in atmospheric particulate matter
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摘要: 大气颗粒物中的水溶性有机物(WSOC)、金属是对自由基有显著贡献的组分,但其生成机制还未明晰。笔者利用电子顺磁共振波谱仪(EPR),结合自由基捕获(BMPO/DMPO)技术,模拟WSOC与金属离子相互作用对自由基生成的影响,结果发现四种典型WSOC(水杨酸,丙二酸,邻苯二甲酸,邻苯二酚)与Fe2 /Fe3 反应的EPR信号能很好吻合大气PM2.5 的BMPO提取液与Fe2 /Fe3 反应生成的自由基信号;进一步拟合液相反应的EPR信号,发现Fe2 与WSOC反应生成烷基类或芳香类自由基,而Fe3 则促进羟基自由基、烷氧自由基、氢过氧自由基、烷基自由基等生成,表明Fe2 、Fe3 与WSOC反应生成自由基的机制不同;随后利用负载Fe的矿质模型颗粒物与邻苯二酚类物质进行液-固反应,发现生成了持久性自由基(EPFRs),再加入DMPO后,却未检测到瞬时自由基,这说明非游离态金属与WSOC可生成EPFRs,而游离态金属能生成瞬时自由基。Abstract: Water-soluble organic matter (WSOC) and metals in atmospheric particulate matter are components that contribute to free radicals significantly, but their formation mechanism is not well understood. In this study, electron paramagnetic resonance spectroscopy (EPR) combined with free radical capture (BMPO/DMPO) technology was used to explore the interaction between WSOC and metal on radical formation. The results showed that the free radicals generated by the reaction of four typical WSOCs (salicylic acid, malonic acid, phthalic acid, catechol) with Fe2 /Fe3 were consistent with the free radicals generated by BMPO extract of PM2.5 and Fe2 /Fe3 . Furthermore, through liquid phase reaction of WSOC with Fe2 /Fe3 , it was found that alkyl or aromatic radicals were formed from Fe2 with WSOC, while Fe3 promoted the formation of hydroxyl radicals, alkoxy radicals, hydroperoxide radicals, alkyl radicals, indicating that the free radical’s formation mechanism by Fe2 and Fe3 was different. Subsequently, liquid-solid reaction of four catechols substances with the Fe-loaded mineral particles was conducted and environmentally persistent free radicals (EPFRs) were obtained and no transient radical formation was detected, which indicates that non-free metals and WSOCs can generate EPFRs, while free metals can generate transient free radicals.
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