Hoffmann Erik H, Tilgner Andreas, Wolke Ralf, Böge Olaf, Walter Arno, Herrmann Hartmut
Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), D-04318 Leipzig, Germany.
Phys Chem Chem Phys. 2018 Apr 25;20(16):10960-10977. doi: 10.1039/c7cp08576a.
Monocyclic aromatic compounds are ubiquitous in the polluted troposphere and contribute to the formation of tropospheric ozone and anthropogenic secondary organic aerosol, including brown carbon. Currently available physico-chemical data including aqueous-phase kinetic and mechanistic data, as well as phase-transfer parameters have been compiled and reviewed, to construct a novel aqueous-phase oxidation mechanism for monocyclic aromatic compounds. The performed chemical mechanism development results in a comprehensive aqueous-phase oxidation mechanism (addressed as CAPRAM-AM1.0), which includes 292 processes considering the oxidation of different aromatic compounds. Detailed numerical simulations with the air parcel model SPACCIM are carried out for different urban environmental and seasonal conditions. Results show that the aqueous-phase chemistry of aromatic compounds, particularly in clouds, increases the organic aerosol mass by up to 10% in total. The absolute contribution to aqSOA in summertime is modelled to be 260 ng m-3 and 1.2 μg m-3 under moderate and strongly polluted conditions, respectively. Aqueous-phase oxidations of aromatic compounds are important not only for the degradation, but also for the formation of nitrated aromatic compounds. In-cloud chemistry contributes up to 54% to the nitrocatechol oxidation and up to 37% to its formation under polluted tropospheric conditions. Besides, nitrated aromatic compounds contribute up to 5.4 μg m-3 to modelled brown carbon concentration in cloud droplets and 140 ng m-3 in aerosol particles. Further, the model simulations indicate that besides OH radical oxidations, aromatic compounds with two hydroxyl groups are also strongly oxidised by O3 and HO2. O3 contributes with 49% to 68% and HO2 with 19% to 22% to the aqueous-phase oxidation of catechol under moderate and strong polluted environmental conditions studied.
单环芳烃在受污染的对流层中普遍存在，对对流层臭氧和包括棕碳在内的人为二次有机气溶胶的形成有贡献。目前已收集并审查了包括水相动力学和机理数据以及相转移参数在内的现有物理化学数据，以构建一种新的单环芳烃水相氧化机制。所进行的化学机制开发产生了一种全面的水相氧化机制（称为CAPRAM-AM1.0），其中包括考虑不同芳烃氧化的292个过程。利用空气包模型SPACCIM针对不同的城市环境和季节条件进行了详细的数值模拟。结果表明，芳烃的水相化学，特别是在云中，使有机气溶胶总量增加了高达10%。在夏季，在中度和重度污染条件下，对水相二次有机气溶胶（aqSOA）的绝对贡献分别模拟为260 ng m-3和1.2 μg m-3。芳烃的水相氧化不仅对其降解很重要，而且对硝化芳烃的形成也很重要。在对流层污染条件下，云内化学对硝基邻苯二酚氧化的贡献高达54%，对其形成的贡献高达37%。此外，硝化芳烃对云滴中模拟的棕碳浓度贡献高达5.4 μg m-3，对气溶胶颗粒中棕碳浓度的贡献为140 ng m-3。此外，模型模拟表明，除了羟基自由基氧化外，具有两个羟基的芳烃也会被臭氧和过氧化氢强烈氧化。在所研究的中度和重度污染环境条件下，臭氧对邻苯二酚水相氧化的贡献为49%至68%，过氧化氢的贡献为19%至22%。
