Iodine's impact on tropospheric oxidants:: a global model study in GEOS-Chem

T. Sherwen; M. J. Evans; L. Carpenter; S. J. Andrews; R. T. Lidster; B. Dix; T. K. Koenig; R. Volkamer; A. Saiz-Lopez; C. Prados-Roman; A. S. Mahajan; C. Ordóñez

doi:10.5194/acpd-15-20957-2015

Iodine's impact on tropospheric oxidants: a global model study in GEOS-Chem

T. Sherwen, M. J. Evans, L. Carpenter, S. J. Andrews, R. T. Lidster, B. Dix, T. K. Koenig, R. Volkamer, A. Saiz-Lopez, C. Prados-Roman, A. S. Mahajan, C. Ordóñez

Chemistry

Research output: Contribution to journal › Article

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 (I₂O_X, X = 2, 3, 4) chemistry, photolysis, deposition and parametrised heterogeneous reactions. In comparisons with recent Iodine Oxide (IO) observations the iodine simulation shows an average bias of +66 % available surface observations in the marine boundary layer (outside of polar regions), and of +73 % within the free troposphere (350 <hPa <900) over the eastern Pacific. Iodine emissions (3.8 Tg yr^minus;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 I_Y 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 O_X loss rate (748 Tg O_X yr^minus;1) is by photolysis of HOI (78 , photolysis of OIO (21 , and reaction of 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 parameters and conclude that the simulation is sensitive to choices in parameterisation of heterogeneous uptake, ocean surface iodide, and I₂O_X (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. This is a significant impact and so halogen chemistry needs to be considered in climate and air quality models.

Original language	English
Pages (from-to)	20957-21023
Number of pages	67
Journal	Atmospheric Chemistry and Physics Discussions
Volume	15
Issue number	15
DOIs	https://doi.org/10.5194/acpd-15-20957-2015
Publication status	Published - 5 Aug 2015

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Sherwen, T., Evans, M. J., Carpenter, L., Andrews, S. J., Lidster, R. T., Dix, B., Koenig, T. K., Volkamer, R., Saiz-Lopez, A., Prados-Roman, C., Mahajan, A. S., & Ordóñez, C. (2015). Iodine's impact on tropospheric oxidants: a global model study in GEOS-Chem. Atmospheric Chemistry and Physics Discussions, 15(15), 20957-21023. https://doi.org/10.5194/acpd-15-20957-2015

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title = "Iodine's impact on tropospheric oxidants:: a global model study in GEOS-Chem",

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 parametrised heterogeneous reactions. In comparisons with recent Iodine Oxide (IO) observations the iodine simulation shows an average bias of +66 % available surface observations in the marine boundary layer (outside of polar regions), and of +73 % within the free troposphere (350 minus;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 rate (748 Tg OX yrminus;1) is by photolysis of HOI (78 , photolysis of OIO (21 , and reaction of 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 parameters and conclude that the simulation is sensitive to choices in parameterisation 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. This is a significant impact and so halogen chemistry needs to be considered in climate and air quality models.",

author = "T. Sherwen and Evans, {M. J.} and L. Carpenter and Andrews, {S. J.} and Lidster, {R. T.} and B. Dix and Koenig, {T. K.} and R. Volkamer and A. Saiz-Lopez and C. Prados-Roman and Mahajan, {A. S.} and C. Ord{\'o}{\~n}ez",

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T1 - Iodine's impact on tropospheric oxidants:

T2 - a global model study in GEOS-Chem

AU - Sherwen, T.

AU - Evans, M. J.

AU - Carpenter, L.

AU - Andrews, S. J.

AU - Lidster, R. T.

AU - Dix, B.

AU - Koenig, T. K.

AU - Volkamer, R.

AU - Saiz-Lopez, A.

AU - Prados-Roman, C.

AU - Mahajan, A. S.

AU - Ordóñez, C.

PY - 2015/8/5

Y1 - 2015/8/5

N2 - 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 parametrised heterogeneous reactions. In comparisons with recent Iodine Oxide (IO) observations the iodine simulation shows an average bias of +66 % available surface observations in the marine boundary layer (outside of polar regions), and of +73 % within the free troposphere (350 minus;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 rate (748 Tg OX yrminus;1) is by photolysis of HOI (78 , photolysis of OIO (21 , and reaction of 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 parameters and conclude that the simulation is sensitive to choices in parameterisation 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. This is a significant impact and so halogen chemistry needs to be considered in climate and air quality models.

AB - 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 parametrised heterogeneous reactions. In comparisons with recent Iodine Oxide (IO) observations the iodine simulation shows an average bias of +66 % available surface observations in the marine boundary layer (outside of polar regions), and of +73 % within the free troposphere (350 minus;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 rate (748 Tg OX yrminus;1) is by photolysis of HOI (78 , photolysis of OIO (21 , and reaction of 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 parameters and conclude that the simulation is sensitive to choices in parameterisation 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. This is a significant impact and so halogen chemistry needs to be considered in climate and air quality models.

U2 - 10.5194/acpd-15-20957-2015

DO - 10.5194/acpd-15-20957-2015

M3 - Article

SN - 1680-7375

VL - 15

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EP - 21023

JO - Atmospheric Chemistry and Physics Discussions

JF - Atmospheric Chemistry and Physics Discussions

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