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Title: Active molecular iodine photochemistry in the Arctic

Journal Article · · Proceedings of the National Academy of Sciences of the United States of America
 [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)

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 (I2) 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 I2 and snowpack iodide (I-) measurements, which were conducted near Utqiagvik, AK, in February 2014. Using chemical ionization mass spectrometry, I2 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 I2 levels are able to significantly increase ozone depletion rates, while also producing iodine monoxide (IO) 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 I2 is likely a dominant source of iodine atoms in the Arctic.

Research Organization:
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States). Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Organization:
USDOE
Grant/Contract Number:
AC05-76RL01830
OSTI ID:
1406742
Report Number(s):
PNNL-SA-129703; 49331; KP1704020
Journal Information:
Proceedings of the National Academy of Sciences of the United States of America, Vol. 114, Issue 38; ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 50 works
Citation information provided by
Web of Science

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Cited By (11)

Direct detection of atmospheric atomic bromine leading to mercury and ozone depletion journal June 2019
A surface-stabilized ozonide triggers bromide oxidation at the aqueous solution-vapour interface text January 2017
A surface-stabilized ozonide triggers bromide oxidation at the aqueous solution-vapour interface journal September 2017
Diurnal cycle of iodine, bromine, and mercury concentrations in Svalbard surface snow journal January 2019
pH-dependent production of molecular chlorine, bromine, and iodine from frozen saline surfaces journal January 2019
Holocene atmospheric iodine evolution over the North Atlantic journal January 2019
Characterization of aerosol growth events over Ellesmere Island during the summers of 2015 and 2016 journal January 2019
Rapid increase in atmospheric iodine levels in the North Atlantic since the mid-20th century journal April 2018
Atmospheric chemistry of iodine anions: elementary reactions of I , IO , and IO 2 with ozone studied in the gas-phase at 300 K using an ion trap journal January 2018
Modeling the Sources and Chemistry of Polar Tropospheric Halogens (Cl, Br, and I) Using the CAM‐Chem Global Chemistry‐Climate Model journal July 2019
Processes Controlling the Composition and Abundance of Arctic Aerosol journal November 2018