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Title: Active molecular iodine photochemistry in the Arctic

Abstract

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 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 I 2 levels are able to significantly increase ozone depletion rates, while also producing iodine monoxide (IO) at levels recently observedmore » in the Arctic. 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:
; ; ; ; ; ; ; ; ; ; ORCiD logo
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1406742
Report Number(s):
PNNL-SA-129703
Journal ID: ISSN 0027-8424; 49331; KP1704020
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Proceedings of the National Academy of Sciences of the United States of America; Journal Volume: 114; Journal Issue: 38
Country of Publication:
United States
Language:
English
Subject:
Environmental Molecular Sciences Laboratory

Citation Formats

Raso, Angela R. W., Custard, Kyle D., May, Nathaniel W., Tanner, David, Newburn, Matt K., Walker, Lawrence, Moore, Ronald J., Huey, L. G., Alexander, Liz, Shepson, Paul B., and Pratt, Kerri A. Active molecular iodine photochemistry in the Arctic. United States: N. p., 2017. Web. doi:10.1073/pnas.1702803114.
Raso, Angela R. W., Custard, Kyle D., May, Nathaniel W., Tanner, David, Newburn, Matt K., Walker, Lawrence, Moore, Ronald J., Huey, L. G., Alexander, Liz, Shepson, Paul B., & Pratt, Kerri A. Active molecular iodine photochemistry in the Arctic. United States. doi:10.1073/pnas.1702803114.
Raso, Angela R. W., Custard, Kyle D., May, Nathaniel W., Tanner, David, Newburn, Matt K., Walker, Lawrence, Moore, Ronald J., Huey, L. G., Alexander, Liz, Shepson, Paul B., and Pratt, Kerri A. 2017. "Active molecular iodine photochemistry in the Arctic". United States. doi:10.1073/pnas.1702803114.
@article{osti_1406742,
title = {Active molecular iodine photochemistry in the Arctic},
author = {Raso, Angela R. W. and Custard, Kyle D. and May, Nathaniel W. and Tanner, David and Newburn, Matt K. and Walker, Lawrence and Moore, Ronald J. and Huey, L. G. and Alexander, Liz and Shepson, Paul B. and Pratt, Kerri A.},
abstractNote = {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. 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.},
doi = {10.1073/pnas.1702803114},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 38,
volume = 114,
place = {United States},
year = 2017,
month = 9
}
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