Department of Chemical Engineering, Columbia University, New York, New York 10027, United States.
Environ Sci Technol. 2020 May 5;54(9):5385-5390. doi: 10.1021/acs.est.9b07485. Epub 2020 Apr 17.
Recent studies have shown the potential of the photosensitizer chemistry of humic acid, as a proxy for humic-like substances in atmospheric aerosols, to contribute to secondary organic aerosol mass. The mechanism requires particle-phase humic acid to absorb solar radiation and become photoexcited, then directly or indirectly oxidize a volatile organic compound (VOC), resulting in a lower volatility product in the particle phase. We performed experiments in a photochemical chamber, with aerosol-phase humic acid as the photosensitizer and limonene as the VOC. In the presence of 26 ppb limonene and under atmospherically relevant UV-visible irradiation levels, there is no significant change in particle diameter. Calculations show that SOA production via this pathway is highly sensitive to VOC precursor concentrations. Under the assumption that HULIS is equally or less reactive than the humic acid used in these experiments, the results suggest that the photosensitizer chemistry of HULIS in ambient atmospheric aerosols is unlikely to be a significant source of secondary organic aerosol mass.
最近的研究表明，腐殖酸的光敏化学性质，作为大气气溶胶中腐殖类物质的一种替代物，有可能促进二次有机气溶胶的形成。该机制需要颗粒状腐殖酸吸收太阳辐射并被光激发，然后直接或间接地氧化挥发性有机化合物（VOC），导致颗粒相中挥发性较低的产物。我们在光化学反应室中进行了实验，以气溶胶态腐殖酸为光敏剂，以柠檬烯为 VOC。在 26 份/十亿的柠檬烯存在下，并在大气相关的紫外-可见辐射水平下，颗粒直径没有明显变化。计算表明，通过这种途径产生的 SOA 对 VOC 前体浓度非常敏感。假设 HULIS 的反应性与本实验中使用的腐殖酸相同或更低，则结果表明，大气气溶胶中 HULIS 的光敏化学性质不太可能成为二次有机气溶胶质量的重要来源。
