Reza Mago, Iezzi Lucia, Finkenzeller Henning, Roose Antoine, Ammann Markus, Volkamer Rainer
Department of Chemistry, University of Colorado Boulder Boulder, Colorado 80309, United States.
Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado Boulder Boulder, Colorado 80309, United States.
ACS Earth Space Chem. 2024 Dec 3;8(12):2495-2508. doi: 10.1021/acsearthspacechem.4c00224. eCollection 2024 Dec 19.
Iodine in the atmosphere destroys ozone and can nucleate particles by formation of iodic acid, HIO. Recent field observations suggest iodate recycles from particles sustaining significant gas-phase IO radical concentrations (0.06 pptv) in aged stratospheric air, and in elevated dust plumes. However, laboratory evidence for iodine activation from aerosols is currently missing. Here, a series of coated-wall flow tube (CWFT) experiments test for iodine release from thin aqueous films containing iodate. Photocatalyzed reactions were studied using iron(III) citrate (Fe-Cit), Arizona Test Dust (ATD), and FeO, along with the dark reaction of iodate with HO at 90% RH and 293 K. Fresh films were separately irradiated with visible and UV-A light, and the efficient release of molecular iodine, I, was observed from all irradiated films containing photocatalysts. For films with Fe-Cit, visible light reduced larger amounts of iodate than UV-A light, activating ∼40% of iodate as I. The formation of oxygenated volatile organic compounds (OVOC) and iodinated OVOC was also observed. Dark exposure of films to HO led to I release in smaller amounts than suggested by Bray-Liebhafsky kinetics, consistent with HO salting-out in the films, or possibly other reasons. Photochemical activation is enhanced by dust proxies in the film, and by aging the film with HO in the dark prior to irradiation. These findings help explain recent field observations of elevated IO radical concentrations in lofted dust layers, and warrant the inclusion of photocatalyzed iodate reduction in atmospheric models.
大气中的碘会破坏臭氧，并可通过形成碘酸（HIO）使颗粒物成核。最近的实地观测表明，在老化的平流层空气中以及扬起的沙尘羽流中，碘酸盐从颗粒物中循环，维持着显著的气相IO自由基浓度（0.06 pptv）。然而，目前缺少气溶胶中碘活化的实验室证据。在此，一系列涂壁流动管（CWFT）实验对含碘酸盐的薄水膜中的碘释放进行了测试。使用柠檬酸铁（Fe-Cit）、亚利桑那测试粉尘（ATD）和FeO研究了光催化反应，以及碘酸盐在90%相对湿度和293 K下与HO的暗反应。分别用可见光和UV-A光照射新鲜薄膜，从所有含光催化剂的照射薄膜中都观察到了分子碘（I）的有效释放。对于含Fe-Cit的薄膜，可见光比UV-A光还原的碘酸盐量更多，约40%的碘酸盐被活化为I。还观察到了氧化挥发性有机化合物（OVOC）和碘化OVOC的形成。薄膜在黑暗中与HO接触导致的I释放量比布雷-利布哈夫斯基动力学所暗示的要少，这与HO在薄膜中的盐析作用一致，也可能是其他原因。薄膜中的沙尘替代物以及在照射前在黑暗中用HO对薄膜进行老化处理可增强光化学活化作用。这些发现有助于解释最近在扬起的沙尘层中IO自由基浓度升高的实地观测结果，并证明在大气模型中纳入光催化碘酸盐还原是合理的。
