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Evaluation of Mixing Height representations in the EUROS model

Evaluatie van menglaag-beschrijvingen in het EUROS model

Synopsis

The EUROS model is an air-quality model used at the Air Research Laborotory of RIVM for short (day) to long term (year) for simulations of the (chemical) dispersion of gaseous and/or airborne particulate matter on European scale. This report describes a part of ongoing development and validation work on the model to improve the models generic applicability which is one of the objectives of the RIVM project compartimental models (now: integration of regional models S711002). It focusses on the representation of dispersion processes, with the goal to improve and evaluate these processes. As such it forms a first step in the revision towards a complete three dimensional description of the transport module in the EUROS model. The work is performed within the framework of a collaboration between the Flemish institute for technological research (VITO) and RIVM. In EUROS the representation of the mixing layer and horizontal advection is improved. The new EUROS version is extensively tested and mixing layer height values are evaluated with lidar measurements. Model results for ozone concentrations and accumulated exposure (AOT) are evaluated in terms of the different mixing layer representations. The revised calculation of the mixing layer gives a much better representation of the land-sea contrast, with lower mixing heights over sea than over land, during the daytime. An important outcome is that the mixing layer concept, used in EUROS, hinders the validation of modelled concentration levels. Because, in spite of the applied scientific model improvements, modelled AOT40 levels for ozone do not show significant improvement in respect to observations. The main concern in this context is the value of the reservoir layer height in the model, which is interlaced with the mixing layer concept. Therefore, it is anticipated that a more realistic representation of the vertical exchange processes, by describing explicitly three-dimensional advection and diffusion, will improve the EUROS model results significantly, both quantitatively and qualitatively.
 

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