Photochemistry of HOSO2 and SO3 and Implications for the Production of Sulfuric Acid

9 pags., 5 figs.
Sulfur trioxide (SO3) and the hydroxysulfonyl radical (HOSO2) are two key intermediates in the production of sulfuric acid (H2SO4) on Earth's atmosphere, one of the major components of acid rain. Here, the photochemical properties of these species are determined by means of high-level quantum chemical methodologies, and the potential impact of their light-induced reactivity is assessed within the context of the conventional acid rain generation mechanism. Results reveal that the photodissociation of HOSO2 occurs primarily in the stratosphere through the ejection of hydroxyl radicals (•OH) and sulfur dioxide (SO2). This may decrease the production rate of H2SO4 in atmospheric regions with low O2 concentration. In contrast, the photostability of SO3 under stratospheric conditions suggests that its removal efficiency, still poorly understood, is key to assess the H2SO4 formation in the upper atmosphere.
The project that gave rise to these results received the support of a fellowship for J.C.-G. from “la Caixa” Foundation (ID 100010434); the fellowship code is LCF/BQ/DR20/11790027. This work was supported by the Spanish “Ministerio de Ciencia e Innovación (MICINN)” (Project ref. CTQ2017-87054-C2-2-P) and Unit of Excellence María de Maeztu CEX2019-000919-M). D.R.-S. is grateful to the Spanish MICINN for the “Ramón y Cajal” grant (ref. RYC2015-19234). A.F.-M. is grateful to the Generalitat Valenciana and the European Social Fund for the postdoctoral contract APOSTD/2019/149 and the project GV/2020/226, and to the MICINN for the “Juan de la Cierva” contract IJC2019-039297-I. Computations have been partially conducted at the local QCEXVAL cluster and the Tirant v3 supercluster (Servei d’Informatica of the University of Valencia).