Intercomparison study of HM models

Recently it was widely recognized that mercury is a hazardous heavy metal, which possesses unique characteristics in the environment. It enters the atmosphere from both anthropogenic and natural sources. It migrates through the environment in different physical-chemical states. It is chemically and biochemically active in soils, water bodies and in the atmosphere. Finally, mercury in the forms of its organic compounds can be accumulated it trophic chains. In these forms it is the most dangerous for human and animals whose diet is connected with fish and other fresh water or oceanic food.

Taking into account high jeopardy of mercury and its high mobility in the environment the 1979 Convention on Long-Range Transboundary Air Pollution included this metal into its consideration. The Protocol on Heavy Metal, which came into effect on December 2004, determines mercury as on of three metals of the first priority. A number of investigations shown that anthropogenic activity of recent centuries led to long-term accumulation of mercury in all main geospheres - the atmosphere, the pedosphere, the Ocean. To assess global biogeochemical aspects of mercury environmental cycle and pollution UNEP launched a project "Global Mercury Assessment".

Complicated mercury behavior in the environment and diversity of its form make study of this metal especially difficult. In such cases numerical modeling becomes a powerful tool of investigations. One should also bears in mind that routine monitoring of mercury is very expensive, and that density of monitoring networks cannot be high. All these facts were recognized by a number of researchers and decision-makers. The Protocol on Heavy Metals considers the modeling approach as a basis for assessment of mercury transboundary pollution in Europe. It determined the main task for the European Monitoring and Evaluation Program (EMEP) in this field as follows: "EMEP shall, using appropriate models …., provide to the Executive Body for the Convention calculations of transboundary fluxes and depositions of heavy metals within the geographical scope of EMEP". According to the Protocol, Meteorological Synthesizing Centre "East" (MSC-E) of EMEP has a responsibility to perform model calculations of transboundary transport and deposition of heavy metals over Europe.

By the moment many numerical models of different types were developed to evaluate mercury atmospheric transport and deposition on local, regional and global levels. They are widely used as purely scientific instruments or as applied methods to solve problems of local or national levels. It is understandable that the models can differ from each other depending on their complexities, their tasks and disposable financial potential. Natural questions arise: Can the models produce reliable results? How far are the modeling results from the available observations? To what extent different models are commensurable between each other?

Recognizing the importance of these questions the Steering Body of EMEP at its 18th session decided (EB.AIR/GE.1/24, 1994) that MSC-E had to organize an intercomparison study of atmospheric long-range transport models for heavy metals. Such a study is considered by the Steering Body to be one of the essential prerequisites for development and application of EMEP operational models. The mercury model intercomparison study was launched in 1999. The mercury intercomparison study is focused on:

- an evaluation of parameterizations of the main physical-chemical processes of mercury transformations in the gaseous and the liquid phase;
- a comparison of modeling results with measurements obtained from both short-term campaigns and from the EMEP monitoring network and other international and national programs;
- a comparison of the main features of long-range transport of different mercury forms.

Taking into account significant complexity of mercury models, necessity to consider main modeling processes separately it was decided to divide the program of the mercury model intercomparison study into three stages:

Stage I

Comparison of modules for physico-chemical transformations of mercury species in a cloud/fog environment with prescribed initial mercury concentrations in ambient air and other physical and chemical parameters relevant for atmospheric mercury transformations.

The stage was started in 1999 and finished in 2001. In addition to the MSC-East four scientific groups from Germany, Sweden and the USA took part in the study. The results were presented in a MSC-East technical report [Ryaboshapko et al,. 2001] and published in scientific literature [Ryaboshapko et al., 2002, Atm. Environ., 36, pp. 3881-3898].

Events
First expert meeting on mercury model comparison 14-15 February 2001, Moscow, Russia

MSC-E Technical Report 2/2001 "Intercomparison Study of Numerical Models for Long-range Atmospheric Transport of Mercury Stage I. Comparison of Chemical Modules for Mercury Transformations in a Cloud/Fog Environment"

Stage II

Comparison of model results with observations during 1-2 weeks episodes. Hourly and daily averages and event based averages of mercury concentrations in air, obtained from the joint Swedish/Canadian/German field campaign TRANSECT 1995 and from the European Union Environment & Climate project Mercury Species Over Europe (MOE-1999) will be used.

This stage started in 2001 was focused on comparison of modeled and observational results. The observations were performed at five measurement sites in Europe during two short-term campaigns in 1995 and 1999. In the first case main attention was paid to the mercury elemental form. In 1999 reactive gaseous and aerosol mercury were measured in addition to the elemental form. Seven scientific groups involved in atmospheric mercury modeling participated in the second stage. They represent all the most advanced scientific and operational mercury models of regional and global types known by the moment. The results of the second stage were analyzed and discussed in MSC-East reports [Artz et al., 2002] and [Ryaboshapko et al., 2003]. A corresponding scientific article is under preparation.

Events
Second expert meeting on Hg model intercomparison 14 - 15 February 2002, Moscow, Russia
Third expert meeting on Hg model intercomparison (Stages II - IV) 15 - 16 April 2003, Moscow, Russia

MSC-E Technical Report 1/2003 "Intercomparison Study of Numerical Models for Long-Range Atmospheric transport of Mercury"

Stage III

The last stage of the mercury model comparison combined performances of seven models of atmospheric mercury transport and deposition of regional and global levels. They are:

GKSS-Forschungszentrum Geesthacht GmbH (Germany), the European mercury version of the
Acid Deposition and Oxidants Model (ADOM).
U.S. Environmental Protection Agency (USA), the Community Multi-Scale Air Quality (CMAQ) model.
Environment Canada (Canada), Global/Regional Atmospheric Heavy Metals Model (GRAHM).
National Ocean and Atmosphere Administration (USA), Hybrid Single Particle Lagrangian Integrated
Trajectory model, version 4 (HYSPLIT_4)
National Institute of Meteorology and Hydrology (Bulgaria), Eulerian Model for Air Pollution (EMAP)
National Environmental Research Institute (Denmark), Danish Eulerian Hemispheric Model (DEHM)
EMEP Meteorological Synthesizing Centre-East, MSCE Heavy Metal model (MSCE-HM).

In this case the EMEP model was presented by two versions: regional one - for EMEP domain, and global one - for the Northern Hemisphere.

The program of the third stage of the study met to the greatest degree the requirements of the 1979 Convention on Long-Range Transboundary Air Pollution. It was focussed on answering two very important questions:

- To what extent can the current atmospheric mercury models of regional and global levels reproduce annual and monthly mean values of mercury concentrations and depositions observed in Central Europe at monitoring stations?
- What is accuracy of model assessment of separate items of mercury atmospheric balances for individual European countries?

To discuss the program of the third stage a workshop was organized in Moscow in April 2003. The participants discussed the volume of calculations, methods of their statistical processing, and formats of reporting data. All details were agreed and accepted as a working plan. The results of the last stage and the study as a whole will be considered by the participants at the final workshop (Moscow, April 2004).

Events
Fourth expert meeting on Hg model intercomparison 22 - 23 April 2004, Moscow, Russia
Minutes

Progress Report 6/2004 "Intercomparison Study of Numerical Models for Long-Range Atmospheric Transport of Mercury"

MSC-E Technical Report 1/2005 "Intercomparison Study of Numerical Models for Long-Range Atmospheric Transport of Mercury. Stage III. Comparison of modeling results with long-term observations and comparison of calculated items of regional balances."