The influence of iodine on the Antarctic stratospheric ozone hole

Abstract

The catalytic depletion of Antarctic stratospheric ozone is linked to anthropogenic emissions of chlorine and bromine. Despite its larger ozone-depleting efficiency, the contribution of ocean-emitted iodine to ozone hole chemistry has not been evaluated, due to the negligible iodine levels previously reported to reach the stratosphere. Based on the recently observed range (0.77 ± 0.1 parts per trillion by volume [pptv]) of stratospheric iodine injection, we use the Whole Atmosphere Community Climate Model to assess the role of iodine in the formation and recent past evolution of the Antarctic ozone hole. Our 1980–2015 simulations indicate that iodine can significantly impact the lower part of the Antarctic ozone hole, contributing, on average, 10% of the lower stratospheric ozone loss during spring (up to 4.2% of the total stratospheric column). We find that the inclusion of iodine advances the beginning and delays the closure stages of the ozone hole by 3 d to 5 d, increasing its area and mass deficit by 11% and 20%, respectively. Despite being present in much smaller amounts, and due to faster gas-phase photochemical reactivation, iodine can dominate (∼73%) the halogen-mediated lower stratospheric ozone loss during summer and early fall, when the heterogeneous reactivation of inorganic chlorine and bromine reservoirs is reduced. The stratospheric ozone destruction caused by 0.77 pptv of iodine over Antarctica is equivalent to that of 3.1 (4.6) pptv of biogenic very short-lived bromocarbons during spring (rest of sunlit period). The relative contribution of iodine to future stratospheric ozone loss is likely to increase as anthropogenic chlorine and bromine emissions decline following the Montreal Protocol.

The gas-phase formation mechanism of iodic acid as an atmospheric aerosol source

“…Field observations and laboratory experiments show that IO 3 − is reduced via iron redox chemistry, H 2 O 2 , nitrite, photosensitized reactions, photolysis and numerous other species (refs. 25,26 and references therein), with the overall effect of recycling iodine to the gas phase. The HIO 3 formation mechanism thus completes a catalytic iodine reaction cycle, by which a single iodine atom can repeatedly form HIO 3 , driving particle formation.…”

“…This chemical reactivity extends to heterogeneous reactions involving aerosol iodide (I − ) 14,15 and iodate (IO 3 − ) (refs. 25,26 and references therein), which is the thermodynamically most stable form of iodine. The efficient multiphase chemistry of IO 3 − is markedly different from that of inert aerosol sulfate (SO 4 2− ), which accumulates without further chemical conversion until it is scavenged from the atmosphere by wet or dry deposition.…”

Solvation, Surface Propensity, and Chemical Reactions of Solutes at Atmospheric Liquid–Vapor Interfaces

“…These aqueous solutions contain halide salt ions but also a variable fraction of organic material from marine biota or after acquiring soluble organic species in the atmosphere . The oxidation of chloride, bromide, and iodide leads to gas-phase species, which significantly affect the ozone budget. , …”

“… 11 The oxidation of chloride, bromide, and iodide leads to gas-phase species, which significantly affect the ozone budget. 12 , 13 …”

Environmental iodine speciation quantification in seawater and snow using ion exchange chromatography and UV spectrophotometric detection

“…The environmental biogeochemistry of iodine, directly and indirectly, impacts our lives, because iodine is both an essential mineral [1] and a regulator of climate through cloud formation and reactions with ozone [2,3]. Iodine is present in a range of chemical forms and understanding why and when it changes speciation is essential for an understanding of its biogeochemical functions.…”