Direct Emission of I_2 Molecule and IO Radical from the Heterogeneous Reactions of Gaseous Ozone with Aqueous Potassium Iodide Solution

Abstract

Recent studies indicated that gaseous halogens mediate key tropospheric chemical processes. The inclusion of halogen-ozone chemistry in atmospheric box models actually closes the ~50% gap between estimated and measured ozone losses in the marine boundary layer. The additional source of gaseous halogens is deemed to involve previously unaccounted for reactions of O_3(g) with sea surface water and marine aerosols. Here, we report that molecular iodine, I_2(g), and iodine monoxide radical, IO(g), are released ([I_2(g)] > 100[IO(g)]) during the heterogeneous reaction of gaseous ozone, O_3(g), with aqueous potassium iodide, KI(aq). It was found that (1) the amounts of I_2(g) and IO(g) produced are directly proportional to [KI(aq)] up to 5 mM and (2) IO(g) yields are independent of bulk pH between 2 and 11, whereas I_2(g) production is markedly enhanced at pH < 4. We propose that O_3(g) reacts with I− at the air/water interface to produce I_2(g) and IO(g) via HOI and IOOO− intermediates, respectively.