气溶胶中溶解性有机质(DOM)液相氧化

许多实验研究都关注大气凝聚相中单一有机化合物的液相光化学，对于实际大气液相环境中溶解性有机质（DOM）的液相光化学氧化的研究还很少.为此，本文报道了模拟太阳光和紫外光辐照下，大气气溶胶水相萃取的DOM直接或·OH氧化的实验结果.不同光解阶段的产物的吸光、氧化特性采用UV-vis和黑炭气溶胶质谱仪（SP-AMS）分析.结果表明，紫外光体系中DOM得到不断降解，相应的产物f44值远低于太阳光体系；液相光解时会生成多种羧酸，草酸的生成量最高.太阳光照反应条件下吸光度和HULIS浓度变化不大；而UV和UV+·OH条件下，HULIS浓度随反应时间不断增加，UV+·OH中反应23 h时HULIS浓度约为初始的4倍，说明含羧基、羟基和芳香基等官能团的棕色碳的形成.综合研究结果表明，太阳光作用下实际DOM液相氧化时吸光性和棕色碳的形成速率不是很快，而紫外光作用下大部分DOM不断分解为HULIS或小分子物质，剩余的有机物的吸光性可能比较强，导致最终产物的单位质量吸收效率（MAE）比较高.本文首次探讨了实际膜液相氧化过程，结果对厘清大气复合污染的形成机制提供重要依据.

Aqueous-phase Oxidation of Dissolved Organic Matter (DOM) from Extracts of Ambient Aerosols

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 f44 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.