Unlike other heavy metals, mercury has been identified to have a long residence time (of the order of one to two years) which makes mercury a global pollutant. This is due to the fact that the most significant form of mercury in the atmosphere, namely elemental mercury exists in gaseous form, it is chemically least reactive, has low solubility in water and takes part in volatilization process at the earth surface. Therefore, a global scale model is an appropriate tool to address the questions such as budgets, long-range transport, trans-boundary exchanges and polar pollution related to mercury in the atmosphere.

Recently at Meteorological Service of Canada (MSC), we have developed a high resolution Global/Regional Atmospheric Heavy Metals Model (GRAHM). GRAHM is an Eulerian Multiscale model and at present it is being used to investigate atmospheric mercury at global scale. The model solves dynamic equations for all meteorological processes and physio-chemical processes for mercury species. The model has variable resolution in vertical and horizontal. By making use of the variable resolution grid in horizontal, the model could be used for simulations on scales from global to urban by placing a high resolution window on a desired region. Gas and aqueous-phase chemistry, multiple-resistance based dry deposition, vertical planetary boundary layer diffusion, cloud-chemical interactions using detailed cloud schemes and wet deposition form the set of mercury processes included in the model. Global anthropogenic emissions of mercury for 1990 available from Global Emission Inventory Activity(GEIA) have been introduced in the model. The model was integrated for multi years to answer some of the questions related to mercury cycling in the atmosphere. Model description and results from the multi-year run will be presented at the conference.