Upper limits of stratospheric IO and OIO inferred from center‐to‐limb‐darkening‐corrected balloon‐borne solar occultation visible spectra: Implications for total gaseous iodine and stratospheric ozone

Abstract

[1] We report upper limits of lower stratospheric IO (inferred lowest values: 0.10 ppt, 0.07 ppt, and 0.06 ppt at 20, 15, and 12.5 km, respectively) and OIO (inferred lowest values: 0.10 ppt, 0.06 ppt, and 0.04 ppt at 20, 15, and 12.5 km, respectively) inferred from balloon-borne solar occultation UV/visible spectroscopy. The spectra were recorded during a series of Laboratoire de Physique Moléculaire et Applications/ differential optical absorption spectroscopy (LPMA/DOAS) balloon flights that were conducted at different geophysical conditions, i.e., inside the Arctic winter vortex, at midlatitudes, and at high latitudes in spring, summer, and fall. Photochemical modeling that accounts for the iodine partitioning during the observations allows us to infer upper limits of total inorganic gas-phase iodine (I y ), i.e., I y (<20 km) of 0.10 ± 0.02 ppt and 0.07 ± 0.01 ppt, taking into account and neglecting OIO photolysis, respectively. For the middle stratosphere, the inferred upper limits of total I y are larger because of the smaller detection sensitivity there. These observations suggest that either much less iodine enters the stratosphere than the amount expected from the stratospheric entry level iodine concentrations (primarily the tropical upper troposphere) or it resides in other minor gaseous species or, eventually, in a nongaseous, i.e., particulate, form in the stratosphere. The implications of our iodine measurements for stratospheric ozone are also briefly assessed using a two-dimensional model. For the assumed loading of 0.1 ppt I y the modeled ozone reduction was small compared to a model run without iodine, with a maximum decrease of around 1% in midlatitudes to high latitudes when OIO photolysis is included. (3334); KEYWORDS: solar occultation spectroscopy, iodine chemistry, stratospheric ozone, center-to-limb-darkening correction, differential optical absorption spectroscopy Citation: Bösch, H., C. Camy-Peyret, M. P. Chipperfield, R. Fitzenberger, H. Harder, U. Platt, and K. Pfeilsticker, Upper limits of stratospheric IO and OIO inferred from center-to-limb-darkening-corrected balloon-borne solar occultation visible spectra: Implications for total gaseous iodine and stratospheric ozone,

Constraints on inorganic gaseous iodine in the tropical upper troposphere and stratosphere inferred from balloon-borne solar occultation observations

“…The spectral retrieval of IO follows the recommendations of Bösch et al (2003) with minor modifications owing to the improved spectral coverage of the spectrometer. The spectral range for IO retrieval is extended to [416 nm, 465 Bösch et al (2003)) covering six strong (5←0, 4←0, 3←0, 2←0, 1←0, 0←0) vibrational bands of the IO A 2 3/2 ←X 2 3/2 electronic transition.…”

“…Here, we use retrievals from solar occultation measurements of the DOAS spectrometer sensitive to the visible spectral range. Spectrometer design is described in detail by Ferlemann et al (2000) and with emphasis on IO and OIO retrievals by Bösch et al (2003). Recently, the instrument has been optimized for IO retrievals by shifting the covered spectral range to shorter wavelengths [400.2 nm, 653.0 nm] such that an additional vibrational excitation band (5←0) of the IO ground state transition to the first electronically excited state (A 2 3/2 ←X 2 3/2 ) centered around 419.5 nm can be used for IO retrievals.…”

“…Murphy et al (1998), Murphy and Thomson (2000), and Murphy et al (2007) indeed found iodine in upper tropospheric and lower stratospheric particles. Most studies investigating the abundances of inorganic iodine species (IO and/or OIO) in the stratosphere conclude undetectably low amounts (Wennberg et al, 1997;Pundt et al, 1998;Bösch et al, 2003;Berthet et al, 2003). To date, the lowest estimate for the upper limit of the total gaseous inorganic iodine (I y ) burden in the high-and mid-latitude lower stratosphere is ∼0.1 ppt (Bösch et al, 2003).…”

“…Most studies investigating the abundances of inorganic iodine species (IO and/or OIO) in the stratosphere conclude undetectably low amounts (Wennberg et al, 1997;Pundt et al, 1998;Bösch et al, 2003;Berthet et al, 2003). To date, the lowest estimate for the upper limit of the total gaseous inorganic iodine (I y ) burden in the high-and mid-latitude lower stratosphere is ∼0.1 ppt (Bösch et al, 2003). The only study claiming detectable amounts of IO in the high-latitude winter stratosphere is Wittrock et al (2000) based on ground-based zenith-sky observations (see discussion in WMO-2006).…”

“…The approach is based on balloon-borne solar absorption spectroscopy as presented by Bösch et al (2003). From spectra recorded in the visible spectral range by a long-path DOAS setup comparable to the one described in Peters et al (2005), we infer IO abundances along a 29 km absorption path in the marine boundary layer between the mainland and an island in the bay of Sao Marcos.…”