Sherwen, T. orcid.org/0000-0002-3006-3876, Evans, M. J. orcid.org/0000-0003-4775-032X, Carpenter, L. J. orcid.org/0000-0002-6257-3950 et al. (11 more authors) (2016) Iodine's impact on tropospheric oxidants:A global model study in GEOS-Chem. Atmospheric Chemistry and Physics. pp. 1161-1186. ISSN 1680-7324
Abstract
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 OXloss 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. 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.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © Authors 2016. This content is made available by the publisher under a Creative Commons Attribution Licence. This means that a user may copy, distribute and display the resource providing that they give credit. Users must adhere to the terms of the licence. |
Dates: |
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Institution: | The University of York |
Academic Units: | The University of York The University of York > Faculty of Sciences (York) > Chemistry (York) |
Depositing User: | Pure (York) |
Date Deposited: | 22 Feb 2016 09:26 |
Last Modified: | 11 Nov 2024 01:13 |
Published Version: | https://doi.org/10.5194/acp-16-1161-2016 |
Status: | Published |
Refereed: | Yes |
Identification Number: | 10.5194/acp-16-1161-2016 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:95475 |
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