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This content will become publicly available on September 5, 2018

Title: Active molecular iodine photochemistry in the Arctic

During springtime, the Arctic atmospheric boundary layer undergoes frequent rapid depletions in ozone and gaseous elemental mercury due to reactions with halogen atoms, influencing atmospheric composition and pollutant fate. Although bromine chemistry has been shown to initiate ozone depletion events, and it has long been hypothesized that iodine chemistry may contribute, no previous measurements of molecular iodine (I 2) have been reported in the Arctic. Iodine chemistry also contributes to atmospheric new particle formation and therefore cloud properties and radiative forcing. Here we present Arctic atmospheric I 2 and snowpack iodide (I -) measurements, which were conducted near Utqiagvik, AK, in February 2014. Using chemical ionization mass spectrometry, I 2 was observed in the atmosphere at mole ratios of 0.3–1.0 ppt, and in the snowpack interstitial air at mole ratios up to 22 ppt under natural sunlit conditions and up to 35 ppt when the snowpack surface was artificially irradiated, suggesting a photochemical production mechanism. Further, snow meltwater I-measurements showed enrichments of up to ~1,900 times above the seawater ratio of I-/Na +, consistent with iodine activation and recycling. Modeling shows that observed I 2 levels are able to significantly increase ozone depletion rates, while also producing iodine monoxide (IO)more » at levels recently observed in the Arctic. Furthermore, these results emphasize the significance of iodine chemistry and the role of snowpack photochemistry in Arctic atmospheric composition, and imply that I 2 is likely a dominant source of iodine atoms in the Arctic.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [5] ;  [5] ;  [4] ;  [5] ;  [2] ; ORCiD logo [3]
  1. Purdue Univ., West Lafayette, IN (United States); Univ. of Michigan, Ann Arbor, MI (United States)
  2. Purdue Univ., West Lafayette, IN (United States)
  3. Univ. of Michigan, Ann Arbor, MI (United States)
  4. Georgia Inst. of Technology, Atlanta, GA (United States)
  5. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
Report Number(s):
PNNL-SA-129703
Journal ID: ISSN 0027-8424; 49331; KP1704020
Grant/Contract Number:
AC05-76RL01830
Type:
Accepted Manuscript
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 114; Journal Issue: 38; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 54 ENVIRONMENTAL SCIENCES; Environmental Molecular Sciences Laboratory; atmosphere; iodine; cryosphere; snowpack; photochemistry
OSTI Identifier:
1406742