Jiang Wenqing, Yu Lu, Yee Lindsay, Chhabra Puneet, Seinfeld John, Anastasio Cort, Zhang Qi
Department of Environmental Toxicology, University of California, Davis, California 95616, United States.
Agricultural and Environmental Chemistry Graduate Group, University of California, Davis, California 95616, United States.
ACS Earth Space Chem. 2024 Oct 10;8(11):2270-2283. doi: 10.1021/acsearthspacechem.4c00204. eCollection 2024 Nov 21.
Phenolic compounds, which are significant emissions from biomass burning (BB), undergo rapid photochemical reactions in both gas and aqueous phases to form secondary organic aerosol, namely, gasSOA and aqSOA, respectively. The formation of gasSOA and aqSOA involves different reaction mechanisms, leading to different product distributions. In this study, we investigate the gaseous and aqueous reactions of guaiacol-a representative BB phenol-to elucidate the compositional differences between phenolic aqSOA and gasSOA. Aqueous-phase reactions of guaiacol produce higher SOA yields than gas-phase reactions (e.g., roughly 60 vs 30% at one half-life of guaiacol). These aqueous reactions involve more complex reaction mechanisms and exhibit a more gradual SOA evolution than their gaseous counterparts. Initially, gasSOA forms with high oxidation levels (O/C > 0.82), while aqSOA starts with lower O/C (0.55-0.75). However, prolonged aqueous-phase reactions substantially increase the oxidation state of aqSOA, making its bulk chemical composition closer to that of gasSOA. Additionally, aqueous reactions form a greater abundance of oligomers and high-molecular-weight compounds, alongside a more sustained production of carboxylic acids. AMS spectral signatures representative of phenolic gasSOA have been identified, which, together with tracer ions of aqSOA, can aid in the interpretation of field observation data on aerosol aging within BB smoke. The notable chemical differences between phenolic gasSOA and aqSOA highlighted in this study also underscore the importance of accurately representing both pathways in atmospheric models to better predict the aerosol properties and their environmental impacts.
酚类化合物是生物质燃烧（BB）的重要排放物，在气相和水相中都会经历快速的光化学反应，分别形成二次有机气溶胶，即气相二次有机气溶胶（gasSOA）和水相二次有机气溶胶（aqSOA）。gasSOA和aqSOA的形成涉及不同的反应机制，导致不同的产物分布。在本研究中，我们研究了愈创木酚（一种典型的生物质燃烧酚类物质）的气相和水相反应，以阐明酚类aqSOA和gasSOA之间的成分差异。愈创木酚的水相反应产生的二次有机气溶胶产率高于气相反应（例如，在愈创木酚的一个半衰期时，大致为60% 对30%）。这些水相反应涉及更复杂的反应机制，并且与气相反应相比，二次有机气溶胶的演化更为缓慢。最初，gasSOA以高氧化水平（O/C > 0.82）形成，而aqSOA则以较低的O/C（0.55 - 0.75）开始。然而，长时间的水相反应会大幅提高aqSOA的氧化态，使其整体化学成分更接近gasSOA。此外，水相反应会形成更大量的低聚物和高分子量化合物，同时羧酸的生成更为持续。已经确定了代表酚类gasSOA的气溶胶质谱特征，其与aqSOA的示踪离子一起，有助于解释生物质燃烧烟雾中气溶胶老化的现场观测数据。本研究中强调的酚类gasSOA和aqSOA之间显著的化学差异也凸显了在大气模型中准确呈现这两种途径对于更好地预测气溶胶特性及其环境影响的重要性。
