A revised global ozone dry deposition estimate based on a new two-layer parameterisation for air–sea exchange and the multi-year MACC composition reanalysis

Abstract. Dry deposition at the Earth's surface is an important sink of atmospheric ozone. Currently, dry deposition of ozone to the ocean surface in atmospheric chemistry models has the largest uncertainty compared to deposition to other surface types, with implications for global tropospheric ozone budget and associated radiative forcing. Most global models assume that the dominant term of surface resistance in the parameterisation of ozone dry deposition velocity at the oceanic surface is constant. There have been recent mechanistic parameterisations for air–sea exchange that account for the simultaneous waterside processes of ozone solubility, molecular diffusion, turbulent transfer, and first-order chemical reaction of ozone with dissolved iodide and other compounds, but there are questions about their performance and consistency. We present a new two-layer parameterisation scheme for the oceanic surface resistance by making the following realistic assumptions: (a) the thickness of the top water layer is of the order of a reaction–diffusion length scale (a few micrometres) within which ozone loss is dominated by chemical reaction and the influence of waterside turbulent transfer is negligible; (b) in the water layer below, both chemical reaction and waterside turbulent transfer act together and are accounted for; and (c) chemical reactivity is present through the depth of the oceanic mixing layer. The new parameterisation has been evaluated against dry deposition velocities from recent open-ocean measurements. It is found that the inclusion of only the aqueous iodide–ozone reaction satisfactorily describes the measurements. In order to better quantify the global dry deposition loss and its interannual variability, modelled 3-hourly ozone deposition velocities are combined with the 3-hourly MACC (Monitoring Atmospheric Composition and Climate) reanalysis ozone for the years 2003–2012. The resulting ozone dry deposition is found to be 98.4 ± 30.0 Tg O3 yr−1 for the ocean and 722.8 ± 87.3 Tg O3 yr−1 globally. The new estimate of the ocean component is approximately a third of the current model estimates. This reduction corresponds to an approximately 20 % decrease in the total global ozone dry deposition, which (with all other components being unchanged) is equivalent to an increase of approximately 5 % in the modelled tropospheric ozone burden and a similar increase in tropospheric ozone lifetime.

Download Full-text

Revising global ozone dry deposition estimates based on a new mechanistic parameterisation for air-sea exchange and the multi-year MACC composition reanalysis

10.5194/acp-2017-768 ◽

2017 ◽

Author(s):

Ashok K. Luhar ◽

Matthew T. Woodhouse ◽

Ian E. Galbally

Keyword(s):

Chemical Reaction ◽

Dry Deposition ◽

Tropospheric Ozone ◽

Surface Resistance ◽

Chemical Reactivity ◽

Deposition Velocity ◽

Water Layer ◽

Turbulent Transfer ◽

Dominant Term ◽

Deposition Velocities

Abstract. Dry deposition at the Earth’s surface is an important sink of atmospheric ozone. Currently, dry deposition of ozone to the ocean surface in atmospheric chemistry models has the largest uncertainty compared to deposition to other surface types, with implications for global tropospheric ozone budget and associated radiative forcing. Most models assume that the dominant term of surface resistance in the parameterisation of ozone dry deposition velocity at the oceanic surface is constant. We present a consistent, process-based parameterisation scheme for air-sea exchange in which the surface resistance accounts for the simultaneous waterside processes of ozone solubility, molecular diffusion, turbulent transfer, and a first-order chemical reaction of ozone with dissolved iodide. The new scheme makes the following realistic assumptions: (a) the thickness of the top water layer is of the order of a reaction-diffusion length scale (a few micrometres) within which ozone loss is dominated by chemical reaction and the influence of waterside turbulent transfer is negligible; (b) in the water layer below, both chemical reaction and waterside turbulent transfer act together and are accounted for; and (c) iodide (hence chemical reactivity) is present through the depth of the oceanic mixing layer. The asymptotic behaviour of the new scheme is consistent with the known limits when either chemical reaction or turbulent transfer dominates. It has been incorporated into the ACCESS-UKCA global chemistry-climate model and the results are evaluated against dry deposition velocities from currently best available open-ocean measurements. In order to better quantify the global dry deposition loss and its interannual variability, the modelled 3-h ozone deposition velocities are combined with the 3-h MACC (Monitoring Atmospheric Composition and Climate) reanalysis ozone for the years 2003–2012. The resulting ozone dry deposition is found to be 98.4 ± 4.5 Tg O3 yr−1 for the ocean and 722.8 ± 20.9 O3 yr−1 globally. The new estimate of the ocean component is approximately a third of the current model estimates. This reduction corresponds to an approximately 20 % decrease in the total global ozone dry deposition, which is equivalent to an increase of approximately 5 % in the modelled tropospheric ozone burden and a similar increase in tropospheric ozone lifetime.

Download Full-text

An improved parameterisation of ozone dry deposition to the ocean and its impact in a global climate-chemistry model

10.5194/acp-2016-844 ◽

2016 ◽

Cited By ~ 1

Author(s):

Ashok K. Luhar ◽

Ian E. Galbally ◽

Matthew T. Woodhouse ◽

Marcus Thatcher

Keyword(s):

Wind Speed ◽

Chemical Reaction ◽

Dry Deposition ◽

Water Surface ◽

Surface Resistance ◽

Global Climate ◽

Deposition Velocity ◽

Turbulent Transfer ◽

Deposition Velocities ◽

The One

Abstract. Schemes used to parameterise ozone dry deposition velocity at the oceanic surface mainly differ in terms of how the dominant term of surface resistance is parameterised. We examine three such schemes and test them in a global climate-chemistry model that incorporates meteorological nudging and monthly-varying reactive-gas emissions. The default scheme invokes the commonly used assumption that the water surface resistance is constant. The other two schemes, named the one-layer and two-layer reactivity schemes, include the simultaneous influence on the water surface resistance of ozone solubility in water, waterside molecular diffusion and turbulent transfer, and a first-order chemical reaction of ozone with dissolved iodide. Unlike the one-layer scheme, the two-layer scheme can indirectly control the degree of interaction between chemical reaction and turbulent transfer through the specification of a surface reactive layer thickness. A comparison is made of the modelled deposition velocity dependencies on sea-surface temperature (SST) and wind speed with recently reported cruise based observations. The default scheme overestimates the observed deposition velocities by a factor of 2 to 4 when the chemical reaction is slow (e.g. under colder SSTs in the Southern Ocean). The default scheme has almost no temperature, wind-speed and latitudinal variations in contrast with the observations. The one-layer scheme provides noticeably better variations, but it overestimates deposition velocity by a factor of 2 to 3 due to an enhancement of the interaction between chemical reaction and turbulent transfer. The two-layer scheme with a surface reactive layer thickness specification of 2.5 microns, which is approximately equal to the reacto-diffusive length scale of the ozone-iodide reaction, is able to simulate the field measurements most closely, with respect to absolute values as well as SST and wind-speed dependence. The two-layer scheme yields the largest deposition velocities in the tropics. The global oceanic deposition of ozone determined using this scheme is approximately 80 Tg yr−1. This amount is 12 % of the modelled total global ozone deposition, is almost half of the original oceanic deposition obtained using the default scheme, and corresponds to a 10 % decrease in the original estimate of the total global ozone deposition. The figure of 12 % is much lower than the previously reported modelled estimate of oceanic deposition being roughly one third of total deposition. Deposition parameterisation influences the predicted ozone mixing ratios, especially in the Southern Hemisphere. For the latitudes 45–70° S, the two-layer scheme improves the prediction of ozone observed at an altitude of 1 km by 7 % and that within the altitude range 1–6 km by 5 % compared to the original scheme.

Download Full-text

An improved parameterisation of ozone dry deposition to the ocean and its impact in a global climate–chemistry model

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-3749-2017 ◽

2017 ◽

Vol 17 (5) ◽

pp. 3749-3767 ◽

Cited By ~ 18

Author(s):

Ashok K. Luhar ◽

Ian E. Galbally ◽

Matthew T. Woodhouse ◽

Marcus Thatcher

Keyword(s):

Wind Speed ◽

Layer Thickness ◽

Chemical Reaction ◽

Dry Deposition ◽

Water Surface ◽

Surface Resistance ◽

Global Climate ◽

Deposition Velocity ◽

Turbulent Transfer ◽

The One

Abstract. Schemes used to parameterise ozone dry deposition velocity at the oceanic surface mainly differ in terms of how the dominant term of surface resistance is parameterised. We examine three such schemes and test them in a global climate–chemistry model that incorporates meteorological nudging and monthly-varying reactive-gas emissions. The default scheme invokes the commonly used assumption that the water surface resistance is constant. The other two schemes, named the one-layer and two-layer reactivity schemes, include the simultaneous influence on the water surface resistance of ozone solubility in water, waterside molecular diffusion and turbulent transfer, and a first-order chemical reaction of ozone with dissolved iodide. Unlike the one-layer scheme, the two-layer scheme can indirectly control the degree of interaction between chemical reaction and turbulent transfer through the specification of a surface reactive layer thickness. A comparison is made of the modelled deposition velocity dependencies on sea surface temperature (SST) and wind speed with recently reported cruise-based observations. The default scheme overestimates the observed deposition velocities by a factor of 2–4 when the chemical reaction is slow (e.g. under colder SSTs in the Southern Ocean). The default scheme has almost no temperature, wind speed, or latitudinal variations in contrast with the observations. The one-layer scheme provides noticeably better variations, but it overestimates deposition velocity by a factor of 2–3 due to an enhancement of the interaction between chemical reaction and turbulent transfer. The two-layer scheme with a surface reactive layer thickness specification of 2.5 µm, which is approximately equal to the reaction-diffusive length scale of the ozone–iodide reaction, is able to simulate the field measurements most closely with respect to absolute values as well as SST and wind-speed dependence. The annual global oceanic deposition of ozone determined using this scheme is approximately half of the original oceanic deposition obtained using the default scheme, and it corresponds to a 10 % decrease in the original estimate of the total global ozone deposition. The previously reported modelled estimate of oceanic deposition is roughly one-third of total deposition and with this new parameterisation it is reduced to 12 % of the modelled total global ozone deposition. Deposition parameterisation influences the predicted atmospheric ozone mixing ratios, especially in the Southern Hemisphere. For the latitudes 45–70° S, the two-layer scheme improves the prediction of ozone observed at an altitude of 1 km by 7 % and that within the altitude range 1–6 km by 5 % compared to the default scheme.

Download Full-text

Update and evaluation of the ozone dry deposition in Oslo CTM3 v1.0

Geoscientific Model Development ◽

10.5194/gmd-12-4705-2019 ◽

2019 ◽

Vol 12 (11) ◽

pp. 4705-4728 ◽

Cited By ~ 1

Author(s):

Stefanie Falk ◽

Amund Søvde Haslerud

Keyword(s):

Dry Deposition ◽

Surface Resistance ◽

Surface Ozone ◽

Ambient Air ◽

Limiting Factors ◽

Canopy Resistance ◽

Ozone Concentrations ◽

Deposition Velocities ◽

The Future ◽

The Impact

Abstract. High concentrations of ozone in ambient air are hazardous not only to humans but to the ecosystem in general. The impact of ozone damage on vegetation and agricultural plants in combination with advancing climate change may affect food security in the future. While the future scenarios in themselves are uncertain, there are limiting factors constraining the accuracy of surface ozone modeling also at present: the distribution and amount of ozone precursors and ozone-depleting substances, the stratosphere–troposphere exchange, as well as scavenging processes. Removal of any substance through gravitational settling or by uptake by plants and soil is referred to as dry deposition. The process of dry deposition is important for predicting surface ozone concentrations and understanding the observed amount and increase of tropospheric background ozone. The conceptual dry deposition velocities are calculated following a resistance-analogous approach, wherein aerodynamic, quasi-laminar, and canopy resistance are key components, but these are hard to measure explicitly. We present an update of the dry deposition scheme implemented in Oslo CTM3. We change from a purely empirical dry deposition parameterization to a more process-based one which takes the state of the atmosphere and vegetation into account. We examine the sensitivity of the scheme to various parameters, e.g., the stomatal conductance-based description of the canopy resistance and the choice of ozone surface resistance, and evaluate the resulting modeled ozone dry deposition with respect to observations and multi-model studies. Individual dry deposition velocities are now available for each land surface type and agree generally well with observations. We also estimate the impact on the modeled ozone concentrations at the surface. We show that the global annual total ozone dry deposition decreases with respect to the previous model version (−37 %), leading to an increase in surface ozone of more than 100 % in some regions. While high sensitivity to changes in dry deposition to vegetation is found in the tropics and the Northern Hemisphere, the largest impact on global scales is associated with the choice of prescribed ozone surface resistance over the ocean and deserts.

Download Full-text

An evaluation of O<sub>3</sub> dry deposition simulations in East Asia

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-919-2014 ◽

2014 ◽

Vol 14 (1) ◽

pp. 919-951 ◽

Cited By ~ 1

Author(s):

R. J. Park ◽

S. K. Hong ◽

H.-A. Kwon ◽

S. Kim ◽

A. Guenther ◽

...

Keyword(s):

East Asia ◽

Atmospheric Chemistry ◽

Dry Deposition ◽

Surface Resistance ◽

Transport Model ◽

Research Area ◽

Chemistry Transport Model ◽

Deposition Velocities ◽

Numerical Studies ◽

High Uncertainty

Abstract. We used a 3-D regional atmospheric chemistry transport model (WRF-Chem) to examine processes that determine O3 in East Asia; in particular, we focused on O3 dry deposition, which is an uncertain research area due to insufficient observation and numerical studies in East Asia. Here, we compare two widely used dry deposition parameterization schemes, Wesely and M3DRY, which are used in the WRF-Chem and CMAQ models, respectively. The O3 dry deposition velocities simulated using the two aforementioned schemes under identical meteorological conditions show considerable differences (a factor of 2) due to surface resistance parameterization discrepancies. The O3 concentration differed by up to 10 ppbv for the monthly mean. The simulated and observed dry deposition velocities were compared, which showed that the Wesely scheme model is consistent with the observations and successfully reproduces the observed diurnal variation. We conduct several sensitivity simulations by changing the land use data, the surface resistance of the water and the model's spatial resolution to examine the factors that affect O3 concentrations in East Asia. As shown, the model was considerably sensitive to the input parameters, which indicates a high uncertainty for such O3 dry deposition simulations. Observations are necessary to constrain the dry deposition parameterization and input data to improve the East Asia air quality models.

Download Full-text