National Synchrotron Radiation Laboratory, School of Nuclear Science and Technology, University of Science and Technology of China, Hefei 230029, China.
Environ Sci Technol. 2012 Apr 3;46(7):3898-904. doi: 10.1021/es204669d. Epub 2012 Mar 19.
Isoprene is a significant source of atmospheric organic aerosol; however, the secondary organic aerosol (SOA) formation and involved chemical reaction pathways have remained to be elucidated. Recent works have shown that the photo-oxidation of isoprene leads to form SOA. In this study, the chemical composition of SOA from the OH-initiated photo-oxidation of isoprene, in the absence of seed aerosols, was investigated through the controlled laboratory chamber experiments. Thermal desorption/tunable vacuum-ultraviolet photoionization time-of-flight aerosol mass spectrometry (TD-VUV-TOF-PIAMS) was used in conjunction with the environmental chamber to study SOA formation. The mass spectra obtained at different photon energies and the photoionization efficiency (PIE) spectra of the SOA products can be obtained in real time. Aided by the ionization energies (IE) either from the ab initio calculations or the literatures, a number of SOA products were proposed. In addition to methacrolein, methyl vinyl ketone, and 3-methyl-furan, carbonyls, hydroxycarbonyls, nitrates, hydroxynitrates, and other oxygenated compounds in SOA formed in laboratory photo-oxiadation experiments were identified, some of them were investigated for the first time. Detailed chemical identification of SOA is crucial for understanding the photo-oxidation mechanisms of VOCs and the eventual formation of SOA. Possible reaction mechanisms will be discussed.
异戊二烯是大气有机气溶胶的重要来源；然而，二次有机气溶胶（SOA）的形成及其涉及的化学反应途径仍有待阐明。最近的研究表明，异戊二烯的光氧化导致 SOA 的形成。在这项研究中，通过控制实验室腔室实验，研究了在没有种子气溶胶的情况下，OH 引发的异戊二烯光氧化产生的 SOA 的化学组成。热解吸/可调真空紫外光电离飞行时间气溶胶质谱（TD-VUV-TOF-PIAMS）与环境腔室一起用于研究 SOA 的形成。可以实时获得不同光子能量下获得的质谱和 SOA 产物的光电离效率（PIE）谱。借助从头计算或文献中的电离能（IE），提出了一些 SOA 产物。除了甲基丙烯醛、甲基乙烯基酮和 3-甲基呋喃外，在实验室光氧化实验中形成的 SOA 中还鉴定出了羰基、羟基羰基、硝酸盐、羟硝酸盐和其他含氧化合物，其中一些是首次进行了研究。对 SOA 的详细化学鉴定对于理解 VOCs 的光氧化机制和 SOA 的最终形成至关重要。将讨论可能的反应机制。
