College of Chemistry and Environmental Engineering, Jiangsu University of Technology, Changzhou 213001, China.
Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, School of Environmental Sciences and Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China.
Sci Total Environ. 2020 Jun 25;723:137953. doi: 10.1016/j.scitotenv.2020.137953. Epub 2020 Mar 14.
In this study, we investigated aqueous-phase triplet excited states (C)-induced photo-degradation of 4-ethylguaiacol (EG) under both simulated sunlight and ultraviolet (UV) light irradiations. Through quencher experiments, the relative contributions of reactive oxygen species (ROS, such as O/O/·OH) and C were calculated and results showed three reactive species, e.g., C, O and O, all seemed to play important roles in the photo-degradation of EG, but contribution from ·OH was relatively minor. High steady-state O concentration after 1 h irradiation further revealed the major contribution of O to photo-degradation under Xe light irradiation. The degradation experiment under three saturated gases (air, O and N) showed that the degradation rate in air-saturated condition was the largest owing to synergistic effect of O and C. Oxidative capacity of aqueous secondary organic aerosol (aqSOA) increased with reaction time by monitoring oxygen-to‑carbon (O/C) ratio and carbon oxidation state (OS) via an aerodyne soot particle aerosol mass spectrometer (SP-AMS). Moreover, aqSOA mass yields were calculated via SP-AMS data. The UV-vis spectral change suggested formation of light-absorbing organics at first stage under simulated sunlight irradiation. Based on the identified products and the reactive intermediates, we postulated that C-induced oxidation might be attributed to direct reactions by C and O, chemical reaction by ROS, as well as oligomerization via H-abstraction. To the best of our knowledge, this is the first time to explore systematically reaction pathways of 4-ethylguaiacol under C radical on the basis of thorough analysis of products and reactive species. Our findings highlight the impacts of aqSOA from biomass burning emissions on air quality and climate change.
在这项研究中，我们研究了模拟阳光和紫外线光照下，C 引发的 4-乙基愈创木酚（EG）水相三重态激发态（C）诱导的光降解。通过猝灭实验，计算了活性氧物质（ROS，如 O/O/·OH）和 C 的相对贡献，结果表明三种活性物质，如 C、O 和 O，似乎都在 EG 的光降解中起重要作用，但·OH 的贡献相对较小。1 小时照射后高稳态 O 浓度进一步表明，在氙灯光照下，O 对光降解的贡献最大。在三种饱和气体（空气、O 和 N）下的降解实验表明，由于 O 和 C 的协同作用，在空气饱和条件下的降解速率最大。通过监测氧碳比（O/C）和碳氧化态（OS），利用飞行时间气溶胶粒子质谱仪（SP-AMS），可以跟踪水相二次有机气溶胶（aqSOA）的氧化能力随时间的变化。此外，通过 SP-AMS 数据计算 aqSOA 质量产率。在模拟阳光照射下，紫外可见光谱的变化首先表明在第一阶段形成了吸光有机物。基于鉴定的产物和反应中间体，我们推测 C 诱导的氧化可能归因于 C 和 O 的直接反应、ROS 的化学反应以及通过 H 抽提的寡聚化。据我们所知，这是首次在彻底分析产物和反应性物质的基础上，系统地探索 4-乙基愈创木酚在 C 自由基下的反应途径。我们的研究结果强调了生物质燃烧排放的 aqSOA 对空气质量和气候变化的影响。
