Impact of biogenic hydrocarbons on tropospheric chemistry: results from a global chemistry-climate model

Abstract. We present a description and evaluation of LMDz-INCA, a global three-dimensional chemistry-climate model, pertaining to its recently developed NMHC version. In this substantially extended version of the model a comprehensive representation of the photochemistry of non-methane hydrocarbons (NMHC) and volatile organic compounds (VOC) from biogenic, anthropogenic, and biomass-burning sources has been included. The tropospheric annual mean methane (9.2 years) and methylchloroform (5.5 years) chemical lifetimes are well within the range of previous modelling studies and are in excellent agreement with estimates established by means of global observations. The model provides a reasonable simulation of the horizontal and vertical distribution and seasonal cycle of CO and key non-methane VOC, such as acetone, methanol, and formaldehyde as compared to observational data from several ground stations and aircraft campaigns. LMDz-INCA in the NMHC version reproduces tropospheric ozone concentrations fairly well throughout most of the troposphere. The model is applied in several sensitivity studies of the biosphere-atmosphere photochemical feedback. The impact of surface emissions of isoprene, acetone, and methanol is studied. These experiments show a substantial impact of isoprene on tropospheric ozone and carbon monoxide concentrations revealing an increase in surface O3 and CO levels of up to 30 ppbv and 60 ppbv, respectively. Isoprene also appears to significantly impact the global OH distribution resulting in a decrease of the global mean tropospheric OH concentration by approximately 0.9×105 molecules cm−3 or roughly 10% and an increase in the global mean tropospheric methane lifetime by approximately four months. A global mean ozone net radiative forcing due to the isoprene induced increase in the tropospheric ozone burden of 0.09W m−2 is found. The key role of isoprene photooxidation in the global tropospheric redistribution of NOx is demonstrated. LMDz-INCA calculates an increase of PAN surface mixing ratios ranging from 75 to 750 pptv and 10 to 250 pptv during northern hemispheric summer and winter, respectively. Acetone and methanol are found to play a significant role in the upper troposphere/lower stratosphere (UT/LS) budget of peroxy radicals. Calculations with LMDz-INCA show an increase in HOx concentrations region of 8 to 15% and 10 to 15% due to methanol and acetone biogenic surface emissions, respectively. The model has been used to estimate the global tropospheric CO budget. A global CO source of 3019 TgCO yr−1 is estimated. This source divides into a primary source of 1533 TgCO yr−1 and secondary source of 1489 TgCO yr−1 deriving from VOC photooxidation. Global VOC-to-CO conversion efficiencies of 90% for methane and between 20 and 45% for individual VOC are calculated by LMDz-INCA.

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Interactive chemistry in the Laboratoire de Météorologie Dynamique general circulation model: model description and impact analysis of biogenic hydrocarbons on tropospheric chemistry

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-2273-2006 ◽

2006 ◽

Vol 6 (8) ◽

pp. 2273-2319 ◽

Cited By ~ 166

Author(s):

G. A. Folberth ◽

D. A. Hauglustaine ◽

J. Lathière ◽

F. Brocheton

Keyword(s):

Tropospheric Ozone ◽

Radiative Forcing ◽

General Circulation ◽

Circulation Model ◽

Tropospheric Chemistry ◽

Model Description ◽

Secondary Source ◽

Substantial Impact ◽

The Impact ◽

Global Mean

Abstract. We present a description and evaluation of LMDz-INCA, a global three-dimensional chemistry-climate model, pertaining to its recently developed NMHC version. In this substantially extended version of the model a comprehensive representation of the photochemistry of non-methane hydrocarbons (NMHC) and volatile organic compounds (VOC) from biogenic, anthropogenic, and biomass-burning sources has been included. The tropospheric annual mean methane (9.2 years) and methylchloroform (5.5 years) chemical lifetimes are well within the range of previous modelling studies and are in excellent agreement with estimates established by means of global observations. The model provides a reasonable simulation of the horizontal and vertical distribution and seasonal cycle of CO and key non-methane VOC, such as acetone, methanol, and formaldehyde as compared to observational data from several ground stations and aircraft campaigns. LMDz-INCA in the NMHC version reproduces tropospheric ozone concentrations fairly well throughout most of the troposphere. The model is applied in several sensitivity studies of the biosphere-atmosphere photochemical feedback. The impact of surface emissions of isoprene, acetone, and methanol is studied. These experiments show a substantial impact of isoprene on tropospheric ozone and carbon monoxide concentrations revealing an increase in surface O3 and CO levels of up to 30 ppbv and 60 ppbv, respectively. Isoprene also appears to significantly impact the global OH distribution resulting in a decrease of the global mean tropospheric OH concentration by approximately 0.7×105 molecules cm-3 or roughly 8% and an increase in the global mean tropospheric methane lifetime by approximately seven months. A global mean ozone net radiative forcing due to the isoprene induced increase in the tropospheric ozone burden of 0.09 W m-2 is found. The key role of isoprene photooxidation in the global tropospheric redistribution of NOx is demonstrated. LMDz-INCA calculates an increase of PAN surface mixing ratios ranging from 75 to 750 pptv and 10 to 250 pptv during northern hemispheric summer and winter, respectively. Acetone and methanol are found to play a significant role in the upper troposphere/lower stratosphere (UT/LS) budget of peroxy radicals. Calculations with LMDz-INCA show an increase in HOx concentrations region of 8 to 15% and 10 to 15% due to methanol and acetone biogenic surface emissions, respectively. The model has been used to estimate the global tropospheric CO budget. A global CO source of 3019 Tg CO yr-1 is estimated. This source divides into a primary source of 1533 Tg CO yr-1 and secondary source of 1489 Tg CO yr-1 deriving from VOC photooxidation. Global VOC-to-CO conversion efficiencies of 90% for methane and between 20 and 45% for individual VOC are calculated by LMDz-INCA.

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Preindustrial-to-present-day radiative forcing by tropospheric ozone from improved simulations with the GISS chemistry-climate GCM

Atmospheric Chemistry and Physics ◽

10.5194/acp-3-1675-2003 ◽

2003 ◽

Vol 3 (5) ◽

pp. 1675-1702 ◽

Cited By ~ 83

Author(s):

D. T. Shindell ◽

G. Faluvegi ◽

N. Bell

Keyword(s):

Tropospheric Ozone ◽

Radiative Forcing ◽

General Circulation ◽

Climate Model ◽

Circulation Model ◽

Tropospheric Chemistry ◽

True Value ◽

Tropopause Region ◽

Dynamics Simulations ◽

Goddard Institute

Abstract. Improved estimates of the radiative forcing from tropospheric ozone increases since the preindustrial have been calculated with the tropospheric chemistry model used at the Goddard Institute for Space Studies (GISS) within the GISS general circulation model (GCM). The chemistry in this model has been expanded to include simplified representations of peroxyacetylnitrates and non-methane hydrocarbons in addition to background NOx-HOx-Ox-CO-CH4 chemistry. The GCM has improved resolution and physics in the boundary layer, improved resolution near the tropopause, and now contains a full representation of stratospheric dynamics. Simulations of present-day conditions show that this coupled chemistry-climate model is better able to reproduce observed tropospheric ozone, especially in the tropopause region, which is critical to climate forcing. Comparison with preindustrial simulations gives a global annual average radiative forcing due to tropospheric ozone increases of 0.30 W/m2 with standard assumptions for preindustrial emissions. Locally, the forcing reaches more than 0.8 W/m2 in parts of the northern subtropics during spring and summer, and is more than 0.6 W/m2 through nearly all the Northern subtropics and mid-latitudes during summer. An alternative preindustrial simulation with soil NOx emissions reduced by two-thirds and emissions of isoprene, paraffins and alkenes from vegetation increased by 50% gives a forcing of 0.33 W/m2. Given the large uncertainties in preindustrial ozone amounts, the true value may lie well outside this range.

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Investigation of strongly enhanced methane Part I: Chemical feedbacks and rapid adjustments.

10.5194/egusphere-egu2020-9786 ◽

2020 ◽

Author(s):

Franziska Winterstein ◽

Patrick Jöckel ◽

Martin Dameris ◽

Michael Ponater ◽

Fabian Tanalski ◽

...

Keyword(s):

Atmospheric Chemistry ◽

Radiative Forcing ◽

Climate Model ◽

Numerical Study ◽

Stratospheric Ozone ◽

Lower Boundary ◽

Tropospheric Chemistry ◽

Substantial Part ◽

Mixing Ratios ◽

The Impact

Methane (CH4) is the second most important greenhouse gas, which atmospheric concentration is influenced by human activities and currently on a sharp rise. We present a study with numerical simulations using a Chemistry-Climate-Model (CCM), which are performed to assess possible consequences of strongly enhanced CH4 concentrations in the Earth's atmosphere for the climate.Our analysis includes experiments with 2xCH4 and 5xCH4 present day (2010) lower boundary mixing ratios using the CCM EMAC. The simulations are conducted with prescribed oceanic conditions, mimicking present day tropospheric temperatures as its changes are largely suppressed. By doing so we are able to investigate the quasi-instantaneous chemical impact on the atmosphere. We find that the massive increase in CH4 strongly influences the tropospheric chemistry by reducing the OH abundance and thereby extending the tropospheric CH4 lifetime as well as the residence time of other chemical pollutants. The region above the tropopause is impacted by a substantial rise in stratospheric water vapor (SWV). The stratospheric ozone (O3) column increases overall, but SWV induced stratospheric cooling also leads to enhanced ozone depletion in the Antarctic lower stratosphere. Regional&#160; patterns of ozone change are affected by modification of stratospheric dynamics, i.e. increased tropical up-welling and stronger meridional transport&#160; towards the polar regions. We calculate the net radiative impact (RI) of the 2xCH4 experiment to be 0.69 W m-2 and for the 5xCH4 experiment to be 1.79 W m-2. A substantial part of the RI is contributed by chemically induced O3 and SWV changes, in line with previous radiative forcing estimates and is for the first time splitted and spatially asigned to its chemical contributors.This numerical study using a CCM with prescibed oceanic conditions shows the rapid responses to significantly enhanced CH4 mixing ratios, which is the first step towards investigating the impact of possible strong future CH4 emissions on atmospheric chemistry and its feedback on climate.

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Implication of extreme atmospheric methane concentrations for chemistry-climate connections

10.5194/acp-2019-41 ◽

2019 ◽

Author(s):

Franziska Winterstein ◽

Fabian Tanalski ◽

Patrick Jöckel ◽

Martin Dameris ◽

Michael Ponater

Keyword(s):

Atmospheric Chemistry ◽

Radiative Forcing ◽

Climate Model ◽

Numerical Study ◽

Stratospheric Ozone ◽

Tropospheric Chemistry ◽

Substantial Part ◽

Atmospheric Concentration ◽

Regional Patterns ◽

The Impact

Abstract. Methane (CH4) is the second most important greenhouse gas, which atmospheric concentration is influenced by human activities. In this study, numerical simulations with a chemistry-climate model (CCM) are performed aiming to assess possible consequences of significantly enhanced CH4 concentrations in the Earth's atmosphere for the climate. We analyze experiments with 2xCH4 and 5xCH4 present day (2010) mixing ratio and its quasi-instantaneous chemical impact on the atmosphere. The massive increase in CH4 strongly influences the tropospheric chemistry by reducing the hydroxyl radical (OH) abundance and thereby extending the CH4 lifetime as well as the residence time of other chemical pollutants. The region above the tropopause is impacted by a substantial rise in stratospheric water vapor (SWV). The stratospheric ozone (O3) column increases overall, but SWV induced stratospheric cooling also leads to a enhanced ozone depletion in the Antarctic lower stratosphere. Regional patterns of ozone change are affected by modification of stratospheric dynamics, i.e. increased tropical up-welling and stronger meridional transport towards the polar regions. We calculate the net radiative impact (RI) of the 2xCH4 experiment to be 0.69 W/m2 and for the 5xCH4 experiment to be 1.79 W/m2. A substantial part of the RI is contributed by chemically induced O3 and SWV changes, in line with previous radiative forcing estimates. To our knowledge this is the first numerical study using a CCM with respect to two/fivefold CH4 concentrations and it is therefore an overdue analysis as it emphasizes the impact of possible strong future CH4 emissions on atmospheric chemistry and its feedback on climate.

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Preindustrial-to-present-day radiative forcing by tropospheric ozone from improved simulations with the GISS chemistry-climate GCM

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-3-3939-2003 ◽

2003 ◽

Vol 3 (4) ◽

pp. 3939-3989 ◽

Cited By ~ 1

Author(s):

D. T. Shindell ◽

G. Faluvegi ◽

N. Bell

Keyword(s):

Tropospheric Ozone ◽

Radiative Forcing ◽

General Circulation ◽

Climate Model ◽

Circulation Model ◽

Tropospheric Chemistry ◽

Climate Forcing ◽

True Value ◽

Tropopause Region ◽

Goddard Institute

Abstract. The tropospheric chemistry model used at the Goddard Institute for Space Studies (GISS) within the GISS general circulation model (GCM) to study interactions between chemistry and climate change has been expanded and integrated into a version of the GCM with higher vertical resolution. The chemistry now includes peroxyacetylnitrates and non-methane hydrocarbons in addition to background NOx-HOx-Ox-CO-CH4 chemistry. The GCM has improved resolution and physics in the boundary layer, improved resolution near the tropopause, and contains a full representation of the stratosphere. Simulations of present-day conditions show that this coupled chemistry-climate model is better able to reproduce observed tropospheric ozone, especially in the tropopause region, which is critical to climate forcing. Comparison with simulations of preindustrial conditions gives a global annual average radiative forcing due to tropospheric ozone increases of 0.30 W/m2 with standard assumptions for preindustrial emissions. Locally, the forcing reaches more than 0.8 W/m2 in parts of the northern subtropics during spring and summer, and is more than 0.6 W/m2 through nearly all the Northern subtropics and mid-latitudes during summer. An alternative preindustrial simulation with soil NOx emissions reduced by two-thirds and emissions of isoprene, paraffins and alkenes from vegetation increased by 50% gives a forcing of 0.33 W/m2. Given the large uncertainties in preindustrial ozone amounts, the true value may lie well outside this range.

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Implication of strongly increased atmospheric methane concentrations for chemistry–climate connections

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-7151-2019 ◽

2019 ◽

Vol 19 (10) ◽

pp. 7151-7163 ◽

Cited By ~ 2

Author(s):

Franziska Winterstein ◽

Fabian Tanalski ◽

Patrick Jöckel ◽

Martin Dameris ◽

Michael Ponater

Keyword(s):

Atmospheric Chemistry ◽

Radiative Forcing ◽

Climate Model ◽

Numerical Study ◽

Stratospheric Ozone ◽

Tropospheric Chemistry ◽

Substantial Part ◽

Atmospheric Concentration ◽

Regional Patterns ◽

The Impact

Abstract. Methane (CH4) is the second-most important directly emitted greenhouse gas, the atmospheric concentration of which is influenced by human activities. In this study, numerical simulations with the chemistry–climate model (CCM) EMAC are performed, aiming to assess possible consequences of significantly enhanced CH4 concentrations in the Earth's atmosphere for the climate. We analyse experiments with 2×CH4 and 5×CH4 present-day (2010) mixing ratio and its quasi-instantaneous chemical impact on the atmosphere. The massive increase in CH4 strongly influences the tropospheric chemistry by reducing the OH abundance and thereby extending the CH4 lifetime as well as the residence time of other chemical substances. The region above the tropopause is impacted by a substantial rise in stratospheric water vapour (SWV). The stratospheric ozone (O3) column increases overall, but SWV-induced stratospheric cooling also leads to a enhanced ozone depletion in the Antarctic lower stratosphere. Regional patterns of ozone change are affected by modification of stratospheric dynamics, i.e. increased tropical upwelling and stronger meridional transport towards the polar regions. We calculate the net radiative impact (RI) of the 2×CH4 experiment to be 0.69 W m−2, and for the 5×CH4 experiment to be 1.79 W m−2. A substantial part of the RH is contributed by chemically induced O3 and SWV changes, in line with previous radiative forcing estimates. To our knowledge this is the first numerical study using a CCM with respect to 2- and 5-fold CH4 concentrations and it is therefore an overdue analysis as it emphasizes the impact of possible strong future CH4 emissions on atmospheric chemistry and its feedback on climate.

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A negative feedback between anthropogenic ozone pollution and enhanced ocean emissions of iodine

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-21917-2014 ◽

2014 ◽

Vol 14 (15) ◽

pp. 21917-21942 ◽

Cited By ~ 3

Author(s):

C. Prados-Roman ◽

C. A. Cuevas ◽

R. P. Fernandez ◽

D. E. Kinnison ◽

J.-F. Lamarque ◽

...

Keyword(s):

Marine Environment ◽

Tropospheric Ozone ◽

Radiative Forcing ◽

Climate Model ◽

Ozone Pollution ◽

Iodine Compounds ◽

Ocean Atmosphere Interaction ◽

Atmosphere Interaction ◽

Inorganic Iodine ◽

The Impact

Abstract. Naturally emitted from the oceans, iodine compounds efficiently destroy atmospheric ozone and reduce its positive radiative forcing effects in the troposphere. Emissions of inorganic iodine have been experimentally shown to depend on the deposition to the oceans of tropospheric ozone, whose concentrations have significantly increased since 1850 as a result of human activities. A chemistry-climate model is used herein to quantify the current ocean emissions of inorganic iodine and assess the impact that the anthropogenic increase of tropospheric ozone has had on the natural cycle of iodine in the marine environment since pre-industrial times. Our results indicate that the human-driven enhancement of tropospheric ozone has doubled the oceanic inorganic iodine emissions following the reaction of ozone with iodide at the sea surface. The consequent build-up of atmospheric iodine, with maximum enhancements of up to 70% with respect to preindustrial times in continental pollution outflow regions, has in turn accelerated the ozone chemical loss over the oceans with strong spatial patterns. We suggest that this ocean–atmosphere interaction represents a negative geochemical feedback loop by which current ocean emissions of iodine act as a natural buffer for ozone pollution and its radiative forcing in the global marine environment.

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Explicit representation of subgrid variability in cloud microphysics yields weaker aerosol indirect effect in the ECHAM5-HAM2 climate model

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-703-2015 ◽

2015 ◽

Vol 15 (2) ◽

pp. 703-714 ◽

Cited By ~ 10

Author(s):

J. Tonttila ◽

H. Järvinen ◽

P. Räisänen

Keyword(s):

Indirect Effect ◽

Radiative Forcing ◽

Climate Model ◽

Cloud Microphysics ◽

Radiation Balance ◽

Anthropogenic Aerosols ◽

Aerosol Indirect Effect ◽

Cloud Activation ◽

The Impact ◽

Global Mean

Abstract. The impacts of representing cloud microphysical processes in a stochastic subcolumn framework are investigated, with emphasis on estimating the aerosol indirect effect. It is shown that subgrid treatment of cloud activation and autoconversion of cloud water to rain reduce the impact of anthropogenic aerosols on cloud properties and thus reduce the global mean aerosol indirect effect by 19%, from −1.59 to −1.28 W m−2. This difference is partly related to differences in the model basic state; in particular, the liquid water path (LWP) is smaller and the shortwave cloud radiative forcing weaker when autoconversion is computed separately for each subcolumn. However, when the model is retuned so that the differences in the basic state LWP and radiation balance are largely eliminated, the global-mean aerosol indirect effect is still 14% smaller (i.e. −1.37 W m−2) than for the model version without subgrid treatment of cloud activation and autoconversion. The results show the importance of considering subgrid variability in the treatment of autoconversion. Representation of several processes in a self-consistent subgrid framework is emphasized. This paper provides evidence that omitting subgrid variability in cloud microphysics contributes to the apparently chronic overestimation of the aerosol indirect effect by climate models, as compared to satellite-based estimates.

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Simulations of preindustrial, present-day, and 2100 conditions in the NASA GISS composition and climate model G-PUCCINI

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-6-4795-2006 ◽

2006 ◽

Vol 6 (3) ◽

pp. 4795-4878 ◽

Cited By ~ 1

Author(s):

D. T. Shindell ◽

G. Faluvegi ◽

N. Unger ◽

E. Aguilar ◽

G. A. Schmidt ◽

...

Keyword(s):

Tropospheric Ozone ◽

Radiative Forcing ◽

Climate Model ◽

Stratospheric Ozone ◽

Atmospheric Composition ◽

Downward Flux ◽

Magnitude Distribution ◽

Rf Values ◽

Goddard Institute ◽

Global Mean

Abstract. A model of atmospheric composition and climate has been developed at the NASA Goddard Institute for Space Studies (GISS) that includes composition seamlessly from the surface to the lower mesosphere. The model is able to capture many features of the observed magnitude, distribution, and seasonal cycle of trace species. The simulation is especially realistic in the troposphere. In the stratosphere, high latitude regions show substantial biases during period when transport governs the distribution as meridional mixing is too rapid in this model version. In other regions, including the extrapolar tropopause region that dominates radiative forcing (RF) by ozone, stratospheric gases are generally well-simulated. The model's stratosphere-troposphere exchange (STE) agrees well with values inferred from observations for both the global mean flux and the ratio of Northern to Southern Hemisphere downward fluxes. Simulations of preindustrial (PI) to present-day (PD) changes show tropospheric ozone burden increases of 11% while the stratospheric burden decreases by 18%. The resulting tropopause RF values are −0.06 W/m2 from stratospheric ozone and 0.40 W/m2 from tropospheric ozone. Global mean mass-weighted OH decreases by 16% from the PI to the PD. STE of ozone also decreased substantially during this time, by 14%. Comparison of the PD with a simulation using 1979 pre-ozone hole conditions for the stratosphere shows a much larger downward flux of ozone into the troposphere in 1979, resulting in a substantially greater tropospheric ozone burden than that seen in the PD run. This implies that reduced STE due to Antarctic ozone depletion may have offset as much as 2/3 of the tropospheric ozone burden increase from PI to PD. However, the model overestimates the downward flux of ozone at high Southern latitudes, so this estimate is likely an upper limit. In the future, the tropospheric ozone burden increases sharply in 2100 for the A1B and A2 scenarios, by 41% and 101%, respectively. The primary reason is enhanced STE, which increases by 71% and 124% in the two scenarios. Chemistry and dry deposition both change so as to reduce ozone, partially in compensation for the enhanced STE. Thus even in the high-pollution A2 scenario, and certainly in A1B, the increased ozone influx dominates the burden changes. However, STE has the greatest influence on middle and high latitudes and towards the upper troposphere, so RF and surface air quality are dominated by emissions. Net RF values due to projected ozone changes depend strongly on the scenario, with 0.1 W/m2 for A1B and 0.8 W/m2 for A2. Changes in oxidation capacity are also scenario dependent, with values of plus and minus seven percent in the A2 and A1B scenarios, respectively.

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A negative feedback between anthropogenic ozone pollution and enhanced ocean emissions of iodine

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-2215-2015 ◽

2015 ◽

Vol 15 (4) ◽

pp. 2215-2224 ◽

Cited By ~ 28

Author(s):

C. Prados-Roman ◽

C. A. Cuevas ◽

R. P. Fernandez ◽

D. E. Kinnison ◽

J-F. Lamarque ◽

...

Keyword(s):

Marine Environment ◽

Tropospheric Ozone ◽

Radiative Forcing ◽

Climate Model ◽

Ozone Pollution ◽

Iodine Compounds ◽

Ocean Atmosphere Interaction ◽

Atmosphere Interaction ◽

Inorganic Iodine ◽

The Impact

Abstract. Naturally emitted from the oceans, iodine compounds efficiently destroy atmospheric ozone and reduce its positive radiative forcing effects in the troposphere. Emissions of inorganic iodine have been experimentally shown to depend on the deposition to the oceans of tropospheric ozone, whose concentrations have significantly increased since 1850 as a result of human activities. A chemistry–climate model is used herein to quantify the current ocean emissions of inorganic iodine and assess the impact that the anthropogenic increase in tropospheric ozone has had on the natural cycle of iodine in the marine environment since pre-industrial times. Our results indicate that the human-driven enhancement of tropospheric ozone has doubled the oceanic inorganic iodine emissions following the reaction of ozone with iodide at the sea surface. The consequent build-up of atmospheric iodine, with maximum enhancements of up to 70% with respect to pre-industrial times in continental pollution outflow regions, has in turn accelerated the ozone chemical loss over the oceans with strong spatial patterns. We suggest that this ocean–atmosphere interaction represents a negative geochemical feedback loop by which current ocean emissions of iodine act as a natural buffer for ozone pollution and its radiative forcing in the global marine environment.

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