Details:

Journal Title:
Atmospheric Chemistry and Physics
Personal Author:
Sherwen, T. ; Evans, M. J. ; Carpenter, L. J. ; Andrews, S. J. ; Lidster, R. T. ; ... More +
Sherwen, T. ; Evans, M. J. ; Carpenter, L. J. ; Andrews, S. J. ; Lidster, R. T. ; Dix, B. ; Koenig, T. K. ; Sinreich, R. ; Ortega, I. ; Volkamer, R. ; Saiz-Lopez, A. ; Prados-Roman, C. ; Mahajan, A. S. ; Ordóñez, C. Less -
NOAA Program & Office:
CIRES (Cooperative Institute for Research in Environmental Sciences)
Description:
We present a global simulation of tropospheric iodine chemistry within the GEOS-Chem chemical transport model. This includes organic and inorganic iodine sources, standard gas-phase iodine chemistry, and simplified higher iodine oxide (I2OX, X = 2, 3, 4) chemistry, photolysis, deposition, and parametrized heterogeneous reactions. In comparisons with recent iodine oxide (IO) observations, the simulation shows an average bias of ∼ +90 % with available surface observations in the marine boundary layer (outside of polar regions), and of ∼ +73 % within the free troposphere (350 hPa < p < 900 hPa) over the eastern Pacific. Iodine emissions (3.8 Tg yr−1) are overwhelmingly dominated by the inorganic ocean source, with 76 % of this emission from hypoiodous acid (HOI). HOI is also found to be the dominant iodine species in terms of global tropospheric IY burden (contributing up to 70 %). The iodine chemistry leads to a significant global tropospheric O3 burden decrease (9.0 %) compared to standard GEOS-Chem (v9-2). The iodine-driven OX loss rate1 (748 Tg OX yr−1) is due to photolysis of HOI (78 %), photolysis of OIO (21 %), and reaction between IO and BrO (1 %). Increases in global mean OH concentrations (1.8 %) by increased conversion of hydroperoxy radicals exceeds the decrease in OH primary production from the reduced O3 concentration. We perform sensitivity studies on a range of parameters and conclude that the simulation is sensitive to choices in parametrization of heterogeneous uptake, ocean surface iodide, and I2OX (X = 2, 3, 4) photolysis. The new iodine chemistry combines with previously implemented bromine chemistry to yield a total bromine- and iodine-driven tropospheric O3 burden decrease of 14.4 % compared to a simulation without iodine and bromine chemistry in the model, and a small increase in OH (1.8 %). This is a significant impact and so halogen chemistry needs to be considered in both climate and air quality models. 1 Here OX is defined as O3 + NO2 + 2NO3 + PAN + PMN+PPN + HNO4 + 3N2O5 + HNO3 + BrO + HOBr + BrNO2+2BrNO3 + MPN + IO + HOI + INO2 + 2INO3 + 2OIO+2I2O2 + 3I2O3 + 4I2O4, where PAN = peroxyacetyl nitrate, PPN = peroxypropionyl nitrate, MPN = methyl peroxy nitrate, and MPN = peroxymethacryloyl nitrate.
Keywords:
[+]
Atmospheric Chemistry Iodine
Source:
Atmospheric Chemistry and Physics, 16(2), 1161-1186
DOI:
https://doi.org/10.5194/acp-16-1161-2016
Document Type:
Journal Article
License:
https://creativecommons.org/licenses/by/3.0/
Rights Information:
CC BY
Compliance:
Library
Main Document Checksum:
[+]
urn:sha256:34c38c521471e7cf271d2bd4e0c5b6de398b103442d1a791ac779ab50307d337
Download URL:
https://repository.library.noaa.gov/view/noaa/51306/noaa_51306_DS1.pdf
File Type:

Supporting Files

• 	Corrigendum	pdf
  	Machine readable version (XML)	xml

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