Multimedia assessment of pollutant pathways in the environment: a Global scale model

摘要

The report describes the assumptions, equations and a few examples of preliminary applications of a global spatial steady-state box model entitled Multimedia Assessment of Pollutant Pathways in the Environment (MAPPE-Global). The model grounds on the concept of already developed European version of MAPPE chemical fate model.MAPPE-Global computes the removal rates of a substance with given physical-chemical properties in an evaluative environment for the Globe with a resolution of 1x1 degree considering atmosphere, land (natural and agriculture soils, forests, impervious surfaces, frozen territories), surface water (including lakes, inland wetlands and reservoirs) and oceans and seas.MAPPE-Global is able to consider chemical emissions in one or more of the environmental compartments and estimates chemical concentrations and fluxes accounting chemical partitioning (gas, liquid or solid), degradation, advective and diffusive transport. At this stage, MAPPE Global does not explicitly compute chemical transport in space, but only the fate of a substance at each location in space. However, the model estimates for each grid cell the mass fluxes of chemical that are available for transport inside or outside of the cell, in addition to concentrations from local emissions. Thus, MAPPE Global is developed specifically to respond questions as: •How will a chemical spread across different media in the different climatic and landscape settings? •How important is the variability of environmental processes in determining the fate of chemicals across the globe? In addition, the model enables estimating, for virtually any location in the world, representative parameters of the environmental removal rates that determine the fate of a contaminant. These rates may be used to feed a zero-dimensional time-dependent model that allows computing the main receptors of the chemical emissions.Besides, in order to evaluate the performance of the MAPPE-Global model a comparison with established models, such as Impact World and USEtox was made by crosschecking of the intermedia removal rate coefficients. Finally, MAPPE-Global was used to quantify for a set of 34 representative pollutants at global scale the range of variability of chemical removal rates for the different environmental compartments and to identify the fate patterns of flyers, swimmers, soil-bound and multimedia chemical substances.