苯水相光氧化反应形成二次有机气溶胶的实验研究

来源于机动车尾气的苯能溶于大气水滴、云雾等水相中并发生水相光氧化反应,在水分蒸发后,产物保留在颗粒相中形成二次有机气溶胶(SOA)粒子.本文采用雾化器将羟基启动苯水相光氧化反应溶液雾化产生气溶胶粒子,通过扩散干燥管除去水蒸气后产生SOA粒子,采用气溶胶激光飞行时间质谱仪进行在线检测,利用紫外可见吸收光谱仪、红外光谱仪和液相色谱串联质谱仪离线测量SOA的化学组分.实验结果表明,激光解吸附质谱中存在醛类(m/z=29(CHO~+)、57(CHOCO~+))、羧酸(m/z=44(COO~+))和苯环(m/z=39(C_3H~+_3)、65(C_5H~-_5))特征裂解碎片峰.SOA粒子的红外光谱图中存在苯环C—H和C=C双键,以及C=O双键、C—O、O—H和C—O—C键的伸缩振动吸收峰,电喷雾电离质谱中存在m/z高达915的离子峰.这表明醛类、羧酸、酚类、芳香醚类产物和酚类产物发生聚合形成的高分子量化合物是SOA粒子的主要化学组分.这为研究人为源挥发性有机化合物水相反应形成SOA的机理提供了实验依据.

Experimental study of the secondary organic aerosol formed from the aqueous photooxidation of benzene

Benzene derived from the exhaust of the motor vehicle can dissolve and undergo photooxidation in water droplets, clouds and other aqueous phase.After evaporation of water, the product remains in the particle phase to form secondary organic aerosol (SOA) particles. The atomizer is used to atomize the solution emerged from the OH-initiated aqueous photooxidation of benzene to form aerosol particles, and SOA particles are generated by removing the water vapor through the diffusion drying tube, its chemical composition is on-line detected by aerosol laser time-of-flight mass spectrometer, and off-line measured with ultraviolet-visible absorption spectrometer, infrared spectrometer and liquid chromatography tandem mass spectrometer, respectively. The experimental results shown that the characteristic fragmentation peaks of aldehydes of m/z=29 (CHO⁺), 57 (CHOCO⁺), carboxylic acid of m/z=44 (COO⁺), and benzene ring of m/z=39 (C₃H₃⁺), 65 (C₅H₅^-) were found in laser desorption mass spectra of SOA particles. The infrared spectrum of SOA particles has stretching vibration absorption peaks of C-H and CC double bonds of benzene ring, CO double bonds, C-O, O-H and C-O-C bonds. What is more, the highest ion peak of m/z=915 was existed in the electrospray ionization mass spectra of SOA particles. These results indicate that aldehydes, carboxylic acids, phenolic compounds, aromatic ethers, and high molecular weight compounds formed from the polymerization of phenolic products are the major chemical components of SOA particles. These provide experimental basis for studying the formation mechanism of SOA formed from aqueous reaction of anthropogenic volatile organic compounds.