Bromine and iodine chemistry in a global chemistry-climate model: description and evaluation of very short-lived oceanic sources

Abstract. The global chemistry-climate model CAM-Chem has been extended to incorporate an expanded bromine and iodine chemistry scheme that includes natural oceanic sources of very short-lived (VSL) halocarbons, gas-phase photochemistry and heterogeneous reactions on aerosols. Ocean emissions of five VSL bromocarbons (CHBr3, CH2Br2, CH2BrCl, CHBrCl2, CHBr2Cl) and three VSL iodocarbons (CH2ICl, CH2IBr, CH2I2) have been parameterised by a biogenic chlorophyll-a (chl-a) dependent source in the tropical oceans (20° N–20° S) as well as constant oceanic fluxes with a 2.5 coast-to-ocean emission ratio for the extratropics (latitudinal bands 20°–50° and 50°–90° in both hemispheres). Top-down emission estimates of bromocarbons have been derived using available measurements in the troposphere and lower stratosphere, while iodocarbons have been constrained with observations in the marine boundary layer (MBL). Emissions of CH3I are based on a previous inventory and the longer lived CH3Br is set to a lower boundary condition. The global oceanic emissions estimated for the most abundant VSL bromocarbons – 533 Gg yr−1 for CHBr3 and 67.3 Gg yr−1 for CH2Br2 – are within the range of previous estimates. Overall the latitudinal and vertical distributions of modelled bromocarbons are in good agreement with observations. Nevertheless, we identify some issues such as the reduced number of aircraft observations to validate models in the Southern Hemisphere, the overestimation of CH2Br2 in the upper troposphere – lower stratosphere and the underestimation of CH3I in the same region. Despite the difficulties involved in the global modelling of the most short-lived iodocarbons (CH2ICl, CH2IBr, CH2I2), modelled results are in good agreement with published observations in the MBL. Finally, sensitivity simulations show that knowledge of the diurnal emission cycle for these species, in particular for CH2I2, is key to assess their global source strength.

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Bromine and iodine chemistry in a global chemistry-climate model: description and evaluation of very short-lived oceanic sources

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-1423-2012 ◽

2012 ◽

Vol 12 (3) ◽

pp. 1423-1447 ◽

Cited By ~ 119

Author(s):

C. Ordóñez ◽

J.-F. Lamarque ◽

S. Tilmes ◽

D. E. Kinnison ◽

E. L. Atlas ◽

...

Keyword(s):

Lower Stratosphere ◽

Marine Boundary Layer ◽

Climate Model ◽

Heterogeneous Reactions ◽

Model Description ◽

Chl A ◽

Tropical Oceans ◽

Vertical Distributions ◽

Iodine Chemistry ◽

Good Agreement

Abstract. The global chemistry-climate model CAM-Chem has been extended to incorporate an expanded bromine and iodine chemistry scheme that includes natural oceanic sources of very short-lived (VSL) halocarbons, gas-phase photochemistry and heterogeneous reactions on aerosols. Ocean emissions of five VSL bromocarbons (CHBr3, CH2Br2, CH2BrCl, CHBrCl2, CHBr2Cl) and three VSL iodocarbons (CH2ICl, CH2IBr, CH2I2) have been parameterised by a biogenic chlorophyll-a (chl-a) dependent source in the tropical oceans (20° N–20° S). Constant oceanic fluxes with 2.5 coast-to-ocean emission ratios are separately imposed on four different latitudinal bands in the extratropics (20°–50° and above 50° in both hemispheres). Top-down emission estimates of bromocarbons have been derived using available measurements in the troposphere and lower stratosphere, while iodocarbons have been constrained with observations in the marine boundary layer (MBL). Emissions of CH3I are based on a previous inventory and the longer lived CH3Br is set to a surface mixing ratio boundary condition. The global oceanic emissions estimated for the most abundant VSL bromocarbons – 533 Gg yr−1 for CHBr3 and 67.3 Gg yr−1 for CH2Br2 – are within the range of previous estimates. Overall the latitudinal and vertical distributions of modelled bromocarbons are in good agreement with observations. Nevertheless, we identify some issues such as the reduced number of aircraft observations to validate models in the Southern Hemisphere, the overestimation of CH2Br2 in the upper troposphere – lower stratosphere and the underestimation of CH3I in the same region. Despite the difficulties involved in the global modelling of the shortest lived iodocarbons (CH2ICl, CH2IBr, CH2I2), modelled results are in good agreement with published observations in the MBL. Finally, sensitivity simulations show that knowledge of the diurnal emission cycle for these species, in particular for CH2I2, is key to assess their global source strength.

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-1161-2016 ◽

2016 ◽

Vol 16 (2) ◽

pp. 1161-1186 ◽

Cited By ~ 51

Author(s):

T. Sherwen ◽

M. J. Evans ◽

L. J. Carpenter ◽

S. J. Andrews ◽

R. T. Lidster ◽

...

Keyword(s):

Marine Boundary Layer ◽

Transport Model ◽

Heterogeneous Reactions ◽

Polar Regions ◽

Chemical Transport Model ◽

Model Study ◽

Sensitivity Studies ◽

Tropospheric O3 ◽

Iodine Chemistry ◽

Inorganic Iodine

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 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.

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Iodine chemistry in the chemistry–climate model SOCOL-AERv2-I

Geoscientific Model Development ◽

10.5194/gmd-14-6623-2021 ◽

2021 ◽

Vol 14 (10) ◽

pp. 6623-6645

Author(s):

Arseniy Karagodin-Doyennel ◽

Eugene Rozanov ◽

Timofei Sukhodolov ◽

Tatiana Egorova ◽

Alfonso Saiz-Lopez ◽

...

Keyword(s):

Lower Stratosphere ◽

Climate Model ◽

Geographical Location ◽

Lower Troposphere ◽

Fold Increase ◽

High Latitudes ◽

Iodine Species ◽

Low Latitudes ◽

Iodine Chemistry ◽

Ozone Column

Abstract. In this paper, we present a new version of the chemistry–climate model SOCOL-AERv2 supplemented by an iodine chemistry module. We perform three 20-year ensemble experiments to assess the validity of the modeled iodine and to quantify the effects of iodine on ozone. The iodine distributions obtained with SOCOL-AERv2-I agree well with AMAX-DOAS observations and with CAM-chem model simulations. For the present-day atmosphere, the model suggests that the iodine-induced chemistry leads to a 3 %–4 % reduction in the ozone column, which is greatest at high latitudes. The model indicates the strongest influence of iodine in the lower stratosphere with 30 ppbv less ozone at low latitudes and up to 100 ppbv less at high latitudes. In the troposphere, the account of the iodine chemistry reduces the tropospheric ozone concentration by 5 %–10 % depending on geographical location. In the lower troposphere, 75 % of the modeled ozone reduction originates from inorganic sources of iodine, 25 % from organic sources of iodine. At 50 hPa, the results show that the impacts of iodine from both sources are comparable. Finally, we determine the sensitivity of ozone to iodine by applying a 2-fold increase in iodine emissions, as it might be representative for iodine by the end of this century. This reduces the ozone column globally by an additional 1.5 %–2.5 %. Our results demonstrate the sensitivity of atmospheric ozone to iodine chemistry for present and future conditions, but uncertainties remain high due to the paucity of observational data of iodine species.

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Evaluated kinetic and photochemical data for atmospheric chemistry: Volume VI – heterogeneous reactions with liquid substrates

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-8045-2013 ◽

2013 ◽

Vol 13 (16) ◽

pp. 8045-8228 ◽

Cited By ~ 95

Author(s):

M. Ammann ◽

R. A. Cox ◽

J. N. Crowley ◽

M. E. Jenkin ◽

A. Mellouki ◽

...

Keyword(s):

Atmospheric Chemistry ◽

Kinetic Data ◽

Lower Stratosphere ◽

Marine Boundary Layer ◽

Chemical Kinetic ◽

Heterogeneous Reactions ◽

Adsorption Parameters ◽

Upper Troposphere ◽

Heterogeneous Processes ◽

Halide Salts

Abstract. This article, the sixth in the ACP journal series, presents data evaluated by the IUPAC Task Group on Atmospheric Chemical Kinetic Data Evaluation. It covers the heterogeneous processes involving liquid particles present in the atmosphere with an emphasis on those relevant for the upper troposphere/lower stratosphere and the marine boundary layer, for which uptake coefficients and adsorption parameters have been presented on the IUPAC website since 2009. The article consists of an introduction and guide to the evaluation, giving a unifying framework for parameterisation of atmospheric heterogeneous processes. We provide summary sheets containing the recommended uptake parameters for the evaluated processes. The experimental data on which the recommendations are based are provided in data sheets in separate appendices for the four surfaces considered: liquid water, deliquesced halide salts, other aqueous electrolytes and sulfuric acid.

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The impact of polar stratospheric ozone loss on Southern Hemisphere stratospheric circulation and climate

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-13705-2014 ◽

2014 ◽

Vol 14 (24) ◽

pp. 13705-13717 ◽

Cited By ~ 31

Author(s):

J. Keeble ◽

P. Braesicke ◽

N. L. Abraham ◽

H. K. Roscoe ◽

J. A. Pyle

Keyword(s):

Southern Hemisphere ◽

Lower Stratosphere ◽

Climate Model ◽

Stratospheric Ozone ◽

Vertical Component ◽

Polar Vortex ◽

Heterogeneous Reactions ◽

Flux Divergence ◽

Ozone Loss ◽

The Impact

Abstract. The impact of polar stratospheric ozone loss resulting from chlorine activation on polar stratospheric clouds is examined using a pair of model integrations run with the fully coupled chemistry climate model UM-UKCA. Suppressing chlorine activation through heterogeneous reactions is found to produce modelled ozone differences consistent with observed ozone differences between the present and pre-ozone hole period. Statistically significant high-latitude Southern Hemisphere (SH) ozone loss begins in August and peaks in October–November, with > 75% of ozone destroyed at 50 hPa. Associated with this ozone destruction is a > 12 K decrease of the lower polar stratospheric temperatures and an increase of > 6 K in the upper stratosphere. The heating components of this temperature change are diagnosed and it is found that the temperature dipole is the result of decreased short-wave heating in the lower stratosphere and increased dynamical heating in the upper stratosphere. The cooling of the polar lower stratosphere leads, through thermal wind balance, to an acceleration of the polar vortex and delays its breakdown by ~ 2 weeks. A link between lower stratospheric zonal wind speed, the vertical component of the Eliassen–Palm (EP) flux, Fz and the residual mean vertical circulation, w*, is identified. In November and December, increased westerly winds and a delay in the breakup of the polar vortex lead to increases in Fz, indicating increased wave activity entering the stratosphere and propagating to higher altitudes. The resulting increase in wave breaking, diagnosed by decreases to the EP flux divergence, drives enhanced downwelling over the polar cap. Many of the stratospheric signals modelled in this study propagate down to the troposphere, and lead to significant surface changes in December.

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Iodine chemistry in the chemistry-climate model SOCOL-AERv2-iodine

10.5194/gmd-2021-107 ◽

2021 ◽

Author(s):

Arseniy Karagodin-Doyennel ◽

Eugene Rozanov ◽

Timofei Sukhodolov ◽

Tatiana Egorova ◽

Alfonso Saiz-Lopez ◽

...

Keyword(s):

Climate Model ◽

Geographical Location ◽

Lower Troposphere ◽

Fold Increase ◽

High Latitudes ◽

Ozone Loss ◽

Low Latitudes ◽

Iodine Chemistry ◽

Ozone Column ◽

Good Agreement

Abstract. This paper introduces a new version of the chemistry-climate model SOCOL-AERv2, supplemented by an iodine chemistry module. We conducted three twenty-year-long ensemble experiments to assess the validity of modeled iodine and to quantify the effects of iodine on ozone. The obtained iodine distributions with SOCOL-AERv2-iodine show good agreement with the CAM-chem model simulations and AMAX-DOAS observations. For the present-day atmosphere, the model suggests the strongest influence of iodine in the lower stratosphere with an ozone loss of up to 30 ppbv at low latitudes and up to 100 ppbv at high latitudes. Globally averaged, the model suggests iodine-induced chemistry to result in an ozone column reduction of 3–4 %, maximizing at high latitudes. In the troposphere, iodine chemistry lowers tropospheric ozone concentrations by 5–10 % depending on the geographical location. We also determined the sensitivity of ozone to iodine applying a 2-fold increase of iodine emissions, which reduces the ozone column globally by an additional 1.5–2.5 %. We found that in the lower troposphere, the share of ozone loss induced by iodine originating from inorganic sources is 75 % and 25 % by iodine originating from organic sources, and contributions become similar at about 50 hPa. These results constrain the importance of atmospheric iodine chemistry for present and future conditions, even though uncertainties remain high due to the paucity of observational data of iodine species.

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

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-20957-2015 ◽

2015 ◽

Vol 15 (15) ◽

pp. 20957-21023 ◽

Cited By ~ 3

Author(s):

T. Sherwen ◽

M. J. Evans ◽

L. J. Carpenter ◽

S. J. Andrews ◽

R. T. Lidster ◽

...

Keyword(s):

Marine Boundary Layer ◽

Transport Model ◽

Heterogeneous Reactions ◽

Polar Regions ◽

Chemical Transport Model ◽

Model Study ◽

Sensitivity Studies ◽

Tropospheric O3 ◽

Iodine Chemistry ◽

Inorganic Iodine

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 < hPa < 900) 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 rate (748 Tg OX yr−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.

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The impact of polar stratospheric ozone loss on Southern Hemisphere stratospheric circulation and climate

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-18049-2014 ◽

2014 ◽

Vol 14 (12) ◽

pp. 18049-18082

Author(s):

J. Keeble ◽

P. Braesicke ◽

N. L. Abraham ◽

H. K. Roscoe ◽

J. A. Pyle

Keyword(s):

Southern Hemisphere ◽

Lower Stratosphere ◽

Climate Model ◽

Stratospheric Ozone ◽

Vertical Component ◽

Polar Vortex ◽

Heterogeneous Reactions ◽

Ozone Loss ◽

Stratospheric Clouds ◽

The Impact

Abstract. The impact of polar stratospheric ozone loss resulting from chlorine activation on polar stratospheric clouds is examined using a pair of model integrations run with the fully coupled chemistry climate model UM-UKCA. Suppressing chlorine activation through heterogeneous reactions is found to produce modelled ozone differences consistent with observed ozone differences between the present and pre-ozone hole period. Statistically significant high latitude Southern Hemisphere (SH) ozone loss begins in August and peaks in October-November, with >75% of ozone destroyed at 50 hPa. Associated with this ozone destruction is a >12 K decrease of the lower polar stratospheric temperatures and an increase of >6 K in the upper stratosphere. The heating components of this temperature change are diagnosed and it is found that the temperature dipole is the result of decreased shortwave heating in the lower stratosphere and increased dynamical heating in the upper stratosphere. The cooling of the polar lower stratosphere leads, through thermal wind balance, to an acceleration of the polar vortex and delays its breakdown by ~2 weeks. A link between lower stratospheric zonal wind speed, the vertical component of the EP flux, Fz, and the residual mean vertical circulation, w*, is identified. In December and January, increased westerly winds lead to increases in Fz, associated with an increase in tropopause height. The resulting increase in wavebreaking leads to enhanced downwelling/reduced upwelling over the polar cap. Many of the stratospheric signals modelled in this study propagate down to the troposphere, and lead to significant surface changes in December.

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