Global mercury modelling at Environment Canada

Summary

We describe the recent developments of Environment Canada's atmospheric mercury model (GRAHM) and its application to the intercontinental source-receptor relationships of mercury. The model includes 2188 Mg yr^-1 global anthropogenic emissions, 1600 Mg yr^-1 terrestrial emissions and 2600 Mg yr^-1 oceanic emissions). Transport, chemical transformation and deposition of Hg⁰, Hg^(II) and Hg(p) are simulated in GRAHM within a meteorological assimilation and forecasting system. Current version of the GRAHM includes GEM oxidation by ozone in the troposphere and halogen oxidation in the Polar and the marine boundary layers. It also includes dynamic exchange of mercury fluxes at air-snow/ice interface. The model simulates springtime atmospheric mercury depletion events (AMDEs) and the net accumulation of mercury in snow in the Polar Regions. We performed one reference simulation with emissions as above and four perturbation simulations with 20% reduced anthropogenic emissions over East Asia, South Asia, Europe and North Africa and North America. 20% reduction in anthropogenic emissions of mercury over East Asia, South Asia, Europe and North Africa and North America represent 7.7%, 1.6%, 2.5% and 1.3% reduction in global anthropogenic emissions respectively. The deposition over East Asia, South Asia, Europe and North America are reduced by 13.5%, 7.9%, 8.3% and 4.3% due to the emission reductions within the same regions. Deposition in North America is found to be most affected by the emission reductions in other regions and the deposition in East Asia is least affected by outside reductions. The deposition in the Arctic is nearly equally sensitive to the unit emission reductions in Europe and East Asia and is most sensitive in springtime due to the high deposition related to AMDEs.