Production of Molecular Iodine and Tri-iodide in the Frozen Solution of Iodide: Implication for Polar Atmosphere

Abstract

The chemistry of reactive halogens in the polar atmosphere plays important roles in ozone and mercury depletion events, oxidizing capacity, and dimethylsulfide oxidation to form cloud-condensation nuclei. Among halogen species, the sources and emission mechanisms of inorganic iodine compounds in the polar boundary layer remain unknown. Here, we demonstrate that the production of tri-iodide (I 3 − ) via iodide oxidation, which is negligible in aqueous solution, is significantly accelerated in frozen solution, both in the presence and the absence of solar irradiation. Field experiments carried out in the Antarctic region (King George Island, 62°13′S, 58°47′W) also showed that the generation of tri-iodide via solar photo-oxidation was enhanced when iodide was added to various ice media. The emission of gaseous I 2 from the irradiated frozen solution of iodide to the gas phase was detected by using cavity ring-down spectroscopy, which was observed both in the frozen state at 253 K and after thawing the ice at 298 K. The accelerated (photo-)oxidation of iodide and the subsequent formation of tri-iodide and I 2 in ice appear to be related with the freeze concentration of iodide and dissolved O 2 trapped in the ice crystal grain boundaries. We propose that an accelerated abiotic transformation of iodide to gaseous I 2 in ice media provides a previously unrecognized formation pathway of active iodine species in the polar atmosphere.

Hindered Amine Light Stabilizers Increase the Stability of Methylammonium Lead Iodide Perovskite Against Light and Oxygen

“…I À ·O 2 may subsequently be excited with near-UV light (l > 350 nm) followedb yo xidation of I À and through variousintermediate reactions leading to the formationo fI 3 À . [18] To furthert est for the formation of I 3 À as ad egradation product, we conducted Raman spectroscopy measurements ( Figure 2c). The Raman spectrum of the as-prepared MAI solution in the low-frequency region shows rise of ab road background withn oR amanf eatures.…”

“…However, the role of light is not straightforward, since I − absorbs below 250 nm, and light of this wavelength is not expected either in daylight or from our light source used for illumination. Based on previously reported data, we assume that I − interacts with O 2 in an oxygen‐saturated solution and forms the charge‐transfer complex (CTC) I − ⋅ O 2 , with a broad absorption at λ =310–360 nm, thus absorbing sunlight. Figure b shows a close‐up of the absorption spectrum recorded in the beginning of the experiment.…”

“…Since this band is also absent in oxygen‐free MAI solution, we attribute it to the I − ⋅ O 2 CTC formed in the dark. I − ⋅ O 2 may subsequently be excited with near‐UV light ( λ >350 nm) followed by oxidation of I − and through various intermediate reactions leading to the formation of I 3 − …”

“…Importantly the process is light induced and does not take place in the dark, suggesting that photoexcitation of I À is the initial step. Oxygen is also crucial, since illuminated solution kept under N 2 does not show absorption changes.H owever, the role of light is not straightforward, since I À absorbs below 250 nm, and light of this wavelength is not expected either in daylighto rf rom our light source used for illumination.B ased on previously reported data, we assume that I À interacts with O 2 in an oxygen-saturated solution and forms the charge-transfer complex (CTC) I À ·O 2 ,w ith ab road absorption at l = 310-360 nm, [17,18] thus absorbing sunlight. Figure 2b shows ac loseup of the absorption spectrum recorded in the beginning of the experiment.…”

Modeling the Sources and Chemistry of Polar Tropospheric Halogens (Cl, Br, and I) Using the CAM‐Chem Global Chemistry‐Climate Model

“…Additionally, the biologically induced release of inorganic iodine (and possibly bromine) from underneath the sea‐ice followed by brine diffusion (Saiz‐Lopez, Boxe, et al, ) can represent the dominant source of iodine (and a nonnegligible source of bromine) to the polar MBL. Likewise, efficient mechanisms of halogen activation of reservoir species occurring on environmental ice and snow have been proposed to represent additional sources (Falk & Sinnhuber, ; Kim et al, , ; O'Driscoll et al, ; O'Sullivan & Sodeau, ; Toyota et al, ). Equivalent recycling reactions occur also on sea‐salt aerosols (Fernandez et al, ; McFiggans et al, ; Vogt et al, ).…”