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A New Approach to Numerical Simulation of the Global Mercury Cycle Based on the Model for Prediction Across Scales
Citation:
Bullock, Orren AND D. Schmeltz. A New Approach to Numerical Simulation of the Global Mercury Cycle Based on the Model for Prediction Across Scales. 2019 International Conference on Mercury as a Global Pollutant (ICMGP 2019), Krakow, POLAND, September 08 - 13, 2019.
Impact/Purpose:
Poster on the potential use of EPA’s next-generation air quality modeling system based on the Model for Prediction Across Scales (MPAS) for building a true multi-media global modeling platform for research and assessment of environmental mercury contamination.
Description:
It is well known that mercury (Hg) cycles through air, water and soil on a global scale. Global-scale modeling of atmospheric Hg has encountered challenges. Relatively coarse spatial discretization is needed to achieve global coverage without incurring excessive computational cost. However, gaseous oxidized mercury is known to deposit from the atmosphere rapidly. Thus, fine-scale modeling is required to address all sources of mercury depositing to specific locations. To achieve this, limited-area models have been applied within global models using various methods to treat the interface between the two. Differences in resolution of time and space, and different treatments of physicochemical processes between the global and regional models can induce unrealistic artifacts. In most cases, feedback effects from the fine scale to the coarse scale are neglected. These problems also affect global simulations of other pollutants. To provide a global air quality model to complement the Community Multiscale Air Quality (CMAQ) model currently available for regional modeling, the U.S. Environmental Protection Agency (EPA) recently began development of a new generation of air quality model based on the Model for Prediction Across Scales (MPAS). MPAS is a global-scale modeling system comprised of separate interoperable programming components, each designed to simulate atmosphere, ocean and other earth-system media in concert. MPAS uses an irregular horizontal grid based on Spherical Centroidal Voronoi Tesselations (SCVTs) producing a mesh of polygonal elements covering the globe without the polar singularities intrinsic to orthogonal grids. During generation of the SCVTs, the mesh element size can be varied based on any desired criteria. Gradual mesh refinement avoids abrupt changes in resolution that have been difficult to treat with traditional grid nesting approaches. Additionally, the same chemical and physical treatments are used in all grid elements and all upscale effects are included. As a first step to developing this next-generation model, it will incorporate the chemical and physical treatments for the pollutant species currently in the CMAQ model, including mercury. Recent advances in CMAQ have added bromine chemistry which could provide additional benefit to mercury simulations. Besides issues related to atmospheric modeling, MPAS could provide a consistent and seamless approach to including the oceans and other earth systems in comprehensive simulations of the entire mercury cycle. The hope for this presentation is to foster international interest in cooperative mercury model development and research using this unified framework to effectively and efficiently improve our understanding of mercury contamination around the globe.
