Research Article

Quantitative detection of iodine in the stratosphere

Theodore K. Koenig, Sunil Baidar, Pedro Campuzano-Jost, Carlos A. Cuevas, Barbara Dix, Rafael P. Fernandez, Hongyu Guo, Samuel R. Hall, Douglas Kinnison, Benjamin A. Nault, Kirk Ullmann, Jose L. Jimenez, Alfonso Saiz-Lopez, and Rainer Volkamer
PNAS January 28, 2020 117 (4) 1860-1866; first published January 13, 2020 https://doi.org/10.1073/pnas.1916828117

  1. Edited by Mark H. Thiemens, University of California San Diego, La Jolla, CA, and approved December 12, 2019 (received for review September 26, 2019)

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Significance

Aircraft measurements in the lower stratosphere indicate iodine is efficient at destroying ozone in the gas and particulate phases. Active iodine chemistry in the upper troposphere–lower stratosphere (UTLS) is the result of convective transport, and efficient multiphase reactions on ice and stratospheric aerosol. Our measurements provide guidance for future technological innovation, laboratory experiments, field observations, and model developments. Global models that simulate the recovery of the ozone layer do not currently consider iodine chemistry. Marine emissions of iodine have increased due to increasing surface ozone in recent decades. This human-induced and increasing iodine source from oceans propagates to the UTLS. Our results posit a possible link between surface air quality, stratospheric ozone loss, and radiative forcing in the UTLS.

Abstract

Oceanic emissions of iodine destroy ozone, modify oxidative capacity, and can form new particles in the troposphere. However, the impact of iodine in the stratosphere is highly uncertain due to the lack of previous quantitative measurements. Here, we report quantitative measurements of iodine monoxide radicals and particulate iodine (Iy,part) from aircraft in the stratosphere. These measurements support that 0.77 ± 0.10 parts per trillion by volume (pptv) total inorganic iodine (Iy) is injected to the stratosphere. These high Iy amounts are indicative of active iodine recycling on ice in the upper troposphere (UT), support the upper end of recent Iy estimates (0 to 0.8 pptv) by the World Meteorological Organization, and are incompatible with zero stratospheric iodine injection. Gas-phase iodine (Iy,gas) in the UT (0.67 ± 0.09 pptv) converts to Iy,part sharply near the tropopause. In the stratosphere, IO radicals remain detectable (0.06 ± 0.03 pptv), indicating persistent Iy,part recycling back to Iy,gas as a result of active multiphase chemistry. At the observed levels, iodine is responsible for 32% of the halogen-induced ozone loss (bromine 40%, chlorine 28%), due primarily to previously unconsidered heterogeneous chemistry. Anthropogenic (pollution) ozone has increased iodine emissions since preindustrial times (ca. factor of 3 since 1950) and could be partly responsible for the continued decrease of ozone in the lower stratosphere. Increasing iodine emissions have implications for ozone radiative forcing and possibly new particle formation near the tropopause.

Footnotes

  • ↵1Present address: Chemical Sciences Division, National Oceanic and Atmospheric Administration, Boulder, CO 80305.

  • ↵2Present address: Cooperative Institute for Research in Environmental Sciences, Boulder, CO 80309.

  • ↵3To whom correspondence may be addressed. Email: rainer.volkamer{at}colorado.edu.

Published under the PNAS license.

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Quantitative detection of iodine in the stratosphere
Theodore K. Koenig, Sunil Baidar, Pedro Campuzano-Jost, Carlos A. Cuevas, Barbara Dix, Rafael P. Fernandez, Hongyu Guo, Samuel R. Hall, Douglas Kinnison, Benjamin A. Nault, Kirk Ullmann, Jose L. Jimenez, Alfonso Saiz-Lopez, Rainer Volkamer
Proceedings of the National Academy of Sciences Jan 2020, 117 (4) 1860-1866; DOI: 10.1073/pnas.1916828117
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Proceedings of the National Academy of Sciences: 117 (4)
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