Peng Weihan, Le Chen, Porter William C, Cocker David R
Department of Chemical and Environmental Engineering, Bourns College of Engineering, University of California, Riverside, Riverside, California 92507, United States.
Bourns College of Engineering, Center for Environmental Research and Technology (CE-CERT), University of California, Riverside, 1084 Columbia Avenue, Riverside, California 92507, United States.
Environ Sci Technol. 2022 Jan 18;56(2):750-760. doi: 10.1021/acs.est.1c04392. Epub 2022 Jan 3.
Current chemical transport models generally use a constant secondary organic aerosol (SOA) yield to represent SOA formation from aromatic compounds under low NO conditions. However, a wide range of SOA yields (10 to 42%) from -xylene under low NO conditions is observed in this study. The chamber HO/RO ratio is identified as a key factor explaining SOA yield variability: higher SOA yields are observed for runs with a higher HO/RO ratio. The RO + RO pathway, which can be increasingly significant under low NO and HO/RO conditions, shows a lower SOA-forming potential compared to the RO + HO pathway. While the traditional low-NO chamber experiments are commonly used to represent the RO + HO pathway, this study finds that the impacts of the RO + RO pathway cannot be ignored under certain conditions. We provide guidance on how to best control for these two pathways in conducting chamber experiments to best obtain SOA yield curves and quantify the contributions from each pathway. On the global scale, the chemical transport model GEOS-Chem is used to identify regions characterized by lower surface HO/RO ratios, suggesting that the RO + RO pathway is more likely to prove significant to overall SOA yields in those regions. Current models generally do not consider the RO + RO impacts on aromatic SOA formation, but preliminary sensitivity tests with updated SOA yield parameters based on such a pathway suggest that without this consideration, some types of SOA may be overestimated in regions with lower HO/RO ratios.
当前的化学传输模型通常使用恒定的二次有机气溶胶（SOA）产率来表示在低NO条件下由芳香族化合物形成的SOA。然而，本研究观察到在低NO条件下，二甲苯的SOA产率范围很广（10%至42%）。实验室内的HO/RO比被确定为解释SOA产率变异性的关键因素：HO/RO比更高的实验运行中观察到更高的SOA产率。在低NO和HO/RO条件下，RO + RO途径可能会变得越来越重要，与RO + HO途径相比，其形成SOA的潜力较低。虽然传统的低NO实验室内实验通常用于代表RO + HO途径，但本研究发现，在某些条件下，RO + RO途径的影响不能被忽视。我们提供了在进行实验室内实验时如何最好地控制这两种途径的指导，以便最好地获得SOA产率曲线并量化每种途径的贡献。在全球范围内，化学传输模型GEOS-Chem用于识别地表HO/RO比更低的区域，这表明RO + RO途径在这些区域对总体SOA产率可能更显著。当前的模型通常不考虑RO + RO对芳香族SOA形成的影响，但基于这种途径使用更新的SOA产率参数进行的初步敏感性测试表明，如果不考虑这一点，在HO/RO比更低的区域，某些类型的SOA可能会被高估。
