Conversion of Iodide to Hypoiodous Acid and Iodine in Aqueous Microdroplets Exposed to Ozone

Halides are incorporated into aerosol sea spray, where they start the catalytic destruction of ozone (O-3) over the oceans and affect the global troposphere. Two intriguing environmental problems undergoing continuous research are (1) to understand how reactive gas phase molecular halogens are directly produced from inorganic halides exposed to O-3 and (2) to constrain the environmental factors that control this interfacial process. This paper presents a laboratory study of the reaction of. O-3 at variable iodide (I-) concentration (0.010-100 mu M) for solutions aerosolized at 25 degrees C, which reveal remarkable differences in the reaction intermediates and products expected in sea spray for low tropospheric [O-3]. The ultrafast oxidation of I- by O-3 at the air-water interface of microdroplets is evidenced by the appearance of hypoiodous acid (HIO), iodite (IO2-), iodate (IO3-), triiodide (I-3(-)), and molecular iodine (I-2). Mass spectrometry measurements reveal an enhancement (up to 28%) in the dissolution of gaseous O-3 at the gas-liquid interface when increasing the concentration of NaI or NaBr from 0.010 to 100 mu M. The production of iodine species such as HIO and I-2 from NaI aerosolized solutions exposed to 50 ppbv O-3 can occur at the air-water interface of sea spray, followed by their transfer to the gas-phase, where they contribute to the loss of tropospheric ozone.