Global modelling framework GLEMOS is a multi-scale multi-pollutant simulation platform recently developed for operational and research applications within the EMEP programme. The framework allows simulations of dispersion and cycling of different classes of pollutants (e.g. heavy metals and persistent organic pollutants) in the environment with a flexible choice of the simulation domain (from global to local scale) and spatial resolution. In addition, GLEMOS supports multi-media description of the pollutants cycling in the environment. A modular architecture of the modelling system allows flexible configuration of the model set-up for particular research task and pollutant properties.

 

Scope of application

GLEMOS modelling system is developed for different research and operational applications including:

  • Multi-media simulations of the environment pollution with various contaminants on different scales (from global to national/local)
  • Estimates of long-term cycling and accumulation of pollutants in the environmental media
  • Assessment of intercontinental transport of the contaminants and its contribution to regional pollution
  • Evaluation of future pollution scenarios and interlinks between climate change and the environment pollution.

 

Modular architecture

General scheme of the modular architecture of
the GLEMOS modelling system

 

The modular architecture is a key feature of the modeling system aimed at providing flexibility for multi-media simulations of pollutants with diverse properties. Each environmental medium is presented in the model by a set of procedures describing general processes in the medium which are combined into the program modules. Each module can be attached to or detached from the model at the compilation stage using command scripts. All pollutants are combined in groups of substances with similar properties (e.g. mercury, particulate heavy metals, POPs etc.). Each pollutant group is presented in the model by a number of modules defining the pollutant properties and its behaviour in each environmental media. Besides, each pollutant can be characterized by different physical forms or chemical compounds specific for each media. The pollutant groups can be attached to the model using the procedure similar to that for the environmental media.

Three major groups of substances have been included into the current version of the modeling system: mercury, particle-bound heavy metals (Pb, Cd) and POPs. An additional pollutant group that is mainly used for testing and evaluation of the model performance pertains to inert and radioactive tracers (131I, 134Cs, 137Cs, 132Te, etc.) It is also planed to include a separate group of modules for simulation of atmospheric aerosol to improve the model description of heavy metal and POP related atmospheric processes (gas-particle partitioning, sorption, heterogeneous chemistry, etc.)

 

Model domain and spatial grid

GLEMOS allows application on different geographical scales with various spatial resolutions. The base model grid on a global scale has horizontal resolution 1°—1°. The grid has variable grid size in the zonal direction next to the poles to avoid extremely small spatial steps (and extra small integration time steps). Starting from the latitude 82° northward and southward, respectively, the grid cells are aggregated to keep the linear step of the grid not smaller than 15 km. Besides, the areas in the immediate vicinity of the poles (within the radius 1°) are presented by single circle grid cells.

In the vertical the model domain covers the height up to 10 hPa (ca. 30 km). Significant vertical coverage is required for modeling atmospheric dispersion of long-lived substances on a global scale in order to avoid the need of setting boundary conditions at the upper boundary as well as to take into account possible stratosphere-troposphere exchange. The current vertical structure consists of 20 irregular terrain-following sigma layers. Among them 10 layers cover the lowest 5 km of the troposphere and height of the lowest layer is about 75 m.

 

Configuration of the horizontal 1°—1° model grid
Vertical structure of the model grid

 

Parameterization of physical and chemical processes

Parameterizations of media processes implemented in the model are largely based on the previous well developed and extensively tested models MSCE-HM and MCSE-POP. A summary of the major model parameterizations is given in the table below.
 
 Process  Description
 Atmosphere

 Advection

 Second-order Bott scheme modified for spherical geometry
 Mass conservation  On-line calculation of vertical velocities using analytical inversion of the Bott scheme
 Eddy diffusion  Second-order implicit finite-difference scheme
 Chemistry (mercury)  Red-ox reactions with O3, OH, Cl, Br, BrO in gas phase and in cloud water
 Gas-particle partitioning (POPs)  Instantaneous equilibrium governed by Junge-Pankow
 Degradation (POPs)  Gas-phase reaction with OH; photodegradation of particle-phase (PAHs)
 Ocean
 Advection  3-time-level second order leapfrog finite-difference scheme
 Partitioning between phases (POPs)  Instantaneous equilibrium governed by partitioning coefficients
 Sedimentation  Based on sedimentation velocity estimated by the Stokes formula
 Degradation (POPs)  First-order process with empirically derived pollutant-dependent degradation rates
 Soil
 Vertical transport  Transport with convective water flux; diffusion and bioturbation
 Partitioning between phases (POPs)  Instantaneous equilibrium governed by partitioning coefficients (readily accessible OC); firs-order dynamic exchange with potentially accessible OC
 Degradation (POPs)  First-order process with empirically derived pollutant-dependent degradation rates
 Media exchange
Dry deposition  Resistance analogy approach, size-segregated deposition velocities of particles
Wet deposition  In-cloud and below-cloud scavenging, empirically derived approach
Gas exchange  Resistence analogy approach, simple two-layers model

 

More detailed descriptions of the model parameterisations and approaches is available in a series of technical reports [Travnikov and Ilyin, 2005; Gusev et al., 2005; Tarrason and Gusev, 2008; Travnikov et al., 2009, Jonson and Travnikov, 2010, Travnikov and Jonson, 2011].

 

Model evaluation

The GELMOS modelling system was extensively evaluated in a number of numerical experiments and multi-model studies within the Task Force on Hemispheric Transport of Air Pollution (TF HTAP). The validation program included testing the atmospheric transport, evaluation of model performance against observations and assessment of source attribution abilities on a global scale. In addition, the atmospheric transport module of GLEMOS was recently tested in a numerical experiment based on dispersion of radioactive isotopes from the Fukushima-1 accident.

 

Further development

Development and update of the GLEMOS modelling system is a continuous process aimed at improvement of the model performance and support of the model parameterisations in the state-of-the-art condition. In particular, nearest model developments will include:

  • Further improvements of the modular architecture including adaptation and testing of the nesting procedure for multi-scale simulations and improvement of the framework computational efficiency;
  • Incorporation of data on aerosols and atmospheric reactants based on external datasets or simplified chemical modules for improving evaluation of HM and POP pollution levels;
  • Preparation of the modelling system for distribution and support as open source software.

 

References

Travnikov O. and I.Ilyin [2005] Regional Model MSCE-HM of Heavy Metal Transboundary Air Pollution in Europe. EMEP/MSC-E Technical Report 6/2005, p.59.

Gusev A., Mantseva E., Shatalov V., Strukov B. [2005] Regional Multicompartment Model MSCE-POP. EMEP/MSC-E Technical Report 5/2005.

Travnikov O., J.E. Jonson, A.S Andersen, M. Gauss, A. Gusev, O. Rozovskaya, D. Simpson, V. Sokovykh, S. Valiyaveetil and P. Wind [2009] Development of the EMEP global modelling framework: Progress report. Joint MSC-E/MSC-W Report. EMEP/MSC-E Technical Report 7/2009.

Jonson J. E. and Travnikov O. (Eds.). [2010] Development of the EMEP global modeling framework: Progress report. Joint MSC-W/MSC-E Report. EMEP/MSC-W Technical Report 1/2010.

Travnikov O. and Jonson J. E. (Eds.). [2011] Global scale modelling within EMEP: Progress report. EMEP/MSC-E Technical Report 1/2011

 

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