Romonosky Dian E, Li Ying, Shiraiwa Manabu, Laskin Alexander, Laskin Julia, Nizkorodov Sergey A
Department of Chemistry, University of California , Irvine, California 92697, United States.
National Institute for Environmental Studies , Tsukuba, Ibaraki 305-8506, Japan.
J Phys Chem A. 2017 Feb 16;121(6):1298-1309. doi: 10.1021/acs.jpca.6b10900. Epub 2017 Feb 6.
Formation of secondary organic aerosols (SOA) from biogenic volatile organic compounds (BVOC) occurs via O- and OH-initiated reactions during the day and reactions with NO during the night. We explored the effect of these three oxidation conditions on the molecular composition and aqueous photochemistry of model SOA prepared from two common BVOC. A common monoterpene, α-pinene, and sesquiterpene, α-humulene, were used to form SOA in a smog chamber via BVOC + O, BVOC + NO, and BVOC + OH + NO oxidation. Samples of SOA were collected on filters, water-soluble compounds from SOA were extracted in water, and the resulting aqueous solutions were photolyzed to simulate the photochemical aqueous processing of SOA. The extent of change in the molecular level composition of SOA over 4 h of photolysis (approximately equivalent to 64 h of photolysis under ambient conditions) was assessed with high-resolution electrospray ionization mass spectrometry. The analysis revealed significant differences in the molecular composition between SOA formed by the different oxidation pathways. The composition further evolved during photolysis with the most notable change corresponding to the nearly complete removal of nitrogen-containing organic compounds. Hydrolysis of SOA compounds also occurred in parallel with photolysis. The preferential loss of larger SOA compounds during photolysis and hydrolysis made the SOA compounds more volatile on average. This study suggests that aqueous processes may under certain conditions lead to a reduction in the SOA loading as opposed to an increase in SOA loading commonly assumed in the literature.
生物源挥发性有机化合物（BVOC）形成二次有机气溶胶（SOA）的过程，在白天通过O和OH引发的反应发生，在夜间则通过与NO的反应发生。我们探究了这三种氧化条件对由两种常见BVOC制备的模型SOA的分子组成和水相光化学的影响。使用一种常见的单萜α-蒎烯和倍半萜α-葎草烯，通过BVOC + O、BVOC + NO和BVOC + OH + NO氧化在烟雾箱中形成SOA。将SOA样品收集在滤纸上，从SOA中提取水溶性化合物并溶于水，然后对所得水溶液进行光解，以模拟SOA的光化学水相处理过程。使用高分辨率电喷雾电离质谱法评估了SOA分子水平组成在4小时光解过程中（大约相当于环境条件下64小时的光解）的变化程度。分析揭示了不同氧化途径形成的SOA在分子组成上存在显著差异。在光解过程中，其组成进一步演变，最显著的变化是含氮有机化合物几乎完全去除。SOA化合物的水解也与光解同时发生。光解和水解过程中较大的SOA化合物优先损失，使得SOA化合物平均挥发性更高。这项研究表明，与文献中通常假设的SOA负载增加相反，水相过程在某些条件下可能导致SOA负载减少。
