Tao Ye, Chen Yan-Tong, Li Nan-Wang, Zhang Xin-Yu, Ye Zhao-Lian, Ge Xin-Lei
School of Chemical and Environmental Engineering, Jiangsu University of Technology, Changzhou 213001, China.
School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Nanjing 210044, China.
Huan Jing Ke Xue. 2021 Jun 8;42(6):2659-2667. doi: 10.13227/j.hjkx.202009162.
Recently, a large number of laboratory studies have focused on the aqueous-phase photochemistry of single organic compound in atmospheric condensed phases, yet few studies have been conducted on the aqueous-phase photochemical oxidation of real-world complex dissolved organic matter (DOM). Therefore, in this work, we report experimental results for the photochemical oxidation of DOM extracts from ambient fine aerosol samples upon direct photolysis or against OH oxidation, under both simulated sunlight and ultraviolet irradiation conditions. The products at different stages of photolysis were analyzed via UV-vis and spectroscopy and soot-particle aerosol mass spectrometry (SP-AMS) to investigate their optical and chemical characteristics. The results demonstrate the effective degradation of DOM under UV irradiation, and the 44 values of the corresponding products aremuch lower than under sunlight irradiation. A variety of carboxylic acids were generated during liquid-phase photolysis, and oxalic acid was found to be the most abundant. The light absorbance and concentration of HULIS did not change significantly under sunlight illumination; however, under UV and UV+·OH conditions, the concentration of HULIS increased continuously with reaction time. The HULIS concentration at 23 h was approximately four times the initial value, indicating the formation of brown carbon species with carboxyl, hydroxyl, and aromatic and other functional groups. Our results show that the increase in light absorptivity and formation rate of brown carbon from DOM are limited when aqueous-phase oxidation occurs under sunlight illumination. In comparison, DOM can constantly decompose into HULIS or small molecules under ultraviolet light illumination, and the light absorptivity of the remaining organic matter may be relatively high, resulting in final products with a high unit mass absorption efficiency (MAE). We have investigated the aqueous-phase oxidation of actual filter extracts for the first time, and our results provide valuable insights to the formation of air pollution complexes.
最近，大量实验室研究聚焦于大气凝聚相中单一有机化合物的水相光化学，但针对实际环境中复杂溶解有机物（DOM）的水相光化学氧化研究却很少。因此，在本研究中，我们报告了在模拟阳光和紫外辐射条件下，对环境细颗粒物样品中DOM提取物进行直接光解或与羟基自由基（OH）氧化反应的光化学氧化实验结果。通过紫外可见光谱和烟尘颗粒气溶胶质谱（SP-AMS）分析光解不同阶段的产物，以研究其光学和化学特性。结果表明，紫外辐射下DOM能有效降解，相应产物的44值远低于阳光照射下的值。液相光解过程中产生了多种羧酸，其中草酸含量最高。在阳光照射下，类腐殖质（HULIS）的吸光度和浓度变化不显著；然而，在紫外和紫外+·OH条件下，HULIS浓度随反应时间持续增加。23小时时HULIS浓度约为初始值的四倍，表明形成了含有羧基、羟基和芳香族等官能团的棕碳物种。我们的结果表明，在阳光照射下水相氧化时，DOM产生的光吸收性增加和棕碳形成速率有限。相比之下，在紫外光照射下，DOM可不断分解为HULIS或小分子，剩余有机物的光吸收性可能相对较高，导致最终产物具有较高的单位质量吸收效率（MAE）。我们首次研究了实际滤膜提取物的水相氧化，研究结果为空气污染复合物的形成提供了有价值的见解。
