The atmospheric column abundance of IO: Implications for stratospheric ozone

Abstract

Abstract. Absorption attributable to atmospheric IO is observed in high-resolution, high air mass solar spectra taken at the National Solar Observatory, Kitt Peak, Arizona, in March 1995. These observations, together with cross sections measured in the laboratory for the IO {A21-I3/2<--X 2H3/2 (2,0) } rotationally resolved electronic transition, are consistent with a total stratospheric i(:dine mixing ratio of 0.2 (+0.3 -0.2) parts per trillion by volume. This result, combined with r, :cent laboratory measurements of the rate of the reactions of IO with other halogen species, suggests that iodine chemistry is not responsible for the reductions observed in lower stratospheric ozone during the last several decades.

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

“…We find upper limits for the concentrations of both gases which put the strongest constraints on their abundance at the region in the Earth's atmosphere where tropospheric air enters the stratosphere to date. Our findings are consistent with previous studies that conclude undetectably low amounts of IO and OIO in the high-and mid-latitude stratosphere (e.g Wennberg et al, 1997;Pundt et al, 1998;Bösch et al, 2003;Berthet et al, 2003). We point out that the inferred upper limits for IO depend on the absorption cross section used for the spectral retrieval.…”

“…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).…”

Injection of iodine to the stratosphere

“…Ground-based observations in Arizona (United States) determined an upper limit for total inorganic iodine (I y ) of 0.2 pptv in the stratosphere [Wennberg et al, 1997]. Balloon-borne UV-Visible spectra derived lower stratospheric upper limits of around 0.1 pptv for both IO and OIO in the northern high and middle latitudes [Bösch et al, 2003], as well as over the tropics [Butz et al, 2009], consistent with previous reports.…”

“…Recent studies have reported values of 0.2-0.4 pptv of iodine monoxide (IO) in the free troposphere over the subtropical station of Izaña in the Atlantic Ocean (Canary Islands) [Puentedura et al, 2012] and 0.1-0.2 pptv range throughout the tropical free troposphere of the Pacific Ocean , demonstrating the ubiquitous presence of the radical in the marine free troposphere. However, due to the low levels of iodine monoxide (IO) previously detected in the lowermost stratosphere at twilight (solar zenith angle (SZA)~90°) [Butz et al, 2009;Wennberg et al, 1997], iodine chemistry is not considered in the photochemistry of stratospheric ozone [WMO, 2014].…”

“…There have been several attempts to detect iodine oxides (IO and OIO) in the upper troposphere-lower stratosphere [Berthet et al, 2003;Bösch et al, 2003;Butz et al, 2009;Pundt et al, 1998;Wennberg et al, 1997;Wittrock et al, 2000]. Ground-based observations in Arizona (United States) determined an upper limit for total inorganic iodine (I y ) of 0.2 pptv in the stratosphere [Wennberg et al, 1997].…”