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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/gmd-2020-139
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gmd-2020-139
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: model description paper 17 Jun 2020

Submitted as: model description paper | 17 Jun 2020

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This preprint is currently under review for the journal GMD.

A revised dry deposition scheme for land-atmosphere exchange of trace gases in ECHAM/MESSy v2.54

Tamara Emmerichs1, Astrid Kerkweg1, Huug Ouwersloot2, Silvano Fares3, Ivan Mammarella4, and Domenico Taraborrelli1 Tamara Emmerichs et al.
  • 1Institute of Energy and Climate Research 8, Troposphere, Forschungszentrum Jülich, Jülich, Germany
  • 2Max Planck Institute for Chemistry, Mainz, Germany
  • 3National Research Council, Institute of Bioeconomy, Rome, Italy
  • 4Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Finland

Abstract. Dry deposition to vegetation is a major sink of ground-level ozone and is responsible for about 20 % of the total tropospheric ozone loss. Its parametrisation in atmospheric chemistry models represent a significant source of uncertainty for the global tropospheric ozone budget and might account for the mismatch with observations. The model used in this study, the Modular Earth Submodel System (MESSy2) linked to ECHAM5 as an atmospheric circulation model (EMAC), is no exception. Like many global models, EMAC employs a “resistance in series” scheme with the major surface deposition via plant stomata which is hardly sensitive to meteorology, depending only on solar radiation. Unlike many global models, however, EMAC uses a simplified high resistance for non-stomatal deposition which makes this pathway negligible in the model. However, several studies have shown this process to be comparable in magnitude to the stomatal uptake, especially during the night over moist surfaces. Hence, we present here a revised dry deposition in EMAC. The default dry deposition scheme has been extended with adjustment factors to predict stomatal responses to temperature and vapour pressure deficit. Furthermore, an explicit formulation of the non-stomatal deposition to the leaf surface (cuticle) dependent on humidity has been implemented based on established schemes. Finally, the soil moisture availability function for plants has been revised to be consistent with the simple hydrological model available in EMAC. This revision was necessary in order to avoid unrealistic stomatal closure where the model shows a strong soil dry bias, e.g. in the Amazon basin in the dry season. These modifications for the three stomatal stress functions have been included in the newly developed MESSy submodel VERTEX, i.e. a process model describing the vertical exchange in the atmospheric boundary layer, which will be evaluated for the first time here. The MESSy submodel describing the dry deposition of trace gases and aerosols (DDEP) has been revised accordingly. The comparison of the simulation results with measurement data at four sites shows that the new scheme enables a more realistic representation of dry deposition. However, the representation is strongly limited by the local meteorology. In total, the changes increase the dry deposition velocity of ozone up to a factor of 2 globally, whereby the highest impact arises from the inclusion of cuticular uptake, especially over moist surfaces. This corresponds to a 6 % increase of global annual dry deposition loss of ozone resulting globally in a slight decrease of ground-level ozone but a regional decrease of up to 25 %. Thus, the revision of the process parameterisation as documented here has the potential to significantly reduce the overestimation of tropospheric ozone in global models.

Tamara Emmerichs et al.

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Tamara Emmerichs et al.

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Measurement data at Lindcove Orange Orchard S. Fares https://doi.org/10.18140/FLX/1440233

Tamara Emmerichs et al.

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Short summary
Dry deposition to vegetation is a major sink of ground-level ozone. Its parametrisation in atmospheric chemistry models represent a significant source of uncertainty for global tropospheric ozone. We extended the current model parametrisation with a relevant pathway and important meteorological adjustment factors. The comparison with measurements shows that this enables a more realistic model representation of ozone dry deposition velocity. Globally, annual dry deposition loss increases.
Dry deposition to vegetation is a major sink of ground-level ozone. Its parametrisation in...
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