应用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

大气颗粒物中的水溶性有机物(WSOC)、金属均是对自由基有显著贡献的组分,但其生成机制还未明晰.本文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.结果表明:4种典型WSOC(水杨酸、丙二酸、邻苯二甲酸、邻苯二酚)标样溶液与Fe^(2+)、Fe^(3+)反应的EPR信号能较好地吻合大气PM_(2.5)的BMPO提取液与Fe^(2+)、Fe^(3+)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,Fe^(2+)与WSOC反应生成烷基类或芳香类自由基,而Fe^(3+)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,说明Fe^(2+)、Fe^(3+)与WSOC反应生成自由基的机制不同.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.研究显示,游离态Fe能与WSOC生成瞬时自由基,非游离态Fe可与WSOC中的邻苯二酚生成稳定的EPFRs,且邻苯二酚取代基的给电子能力越强,EPFRs越容易生成,但其无法转化为瞬时自由基.

Water-soluble organic matter(WSOC)and metals in atmospheric particulate matter are components that contribute to the formation of free radicals significantly,but their formation mechanisms are not well understood.In this study,electron paramagnetic resonance spectroscopy(EPR)combined with free radical capture(BMPO/DMPO)technology was used to explore the effect of 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 Fe^(2+)and Fe^(3+) were consistent with the free radicals generated by BMPO extract of PM_(2.5) and Fe^(2+),Fe^(3+).Furthermore,through liquid phase reaction of WSOC with Fe^(2+)and Fe^(3+),it was found that alkyl or aromatic radicals were formed from Fe2+with WSOC,while Fe^(3+) promoted the formation of hydroxyl radicals,alkoxy radicals,hydroperoxide radicals,alkyl radicals,indicating that the free radical’s formation mechanisms by Fe^(2+)and Fe^(3+)were different.Subsequently,liquid-solid reaction of four catechol substances with the Fe-loaded mineral particles was conducted and environmentally persistent free radicals(EPFRs)were obtained,and no transient radical formation was detected.This study has shown that free Fe can generate instantaneous free radicals with WSOC,non-free Fe can generate stable EPFRs with catechol in WSOC,and the stronger the electron-donating ability of catechol substituents,the easier the EPFRs are formed,but EPFRs cannot be converted into instantaneous free radicals.