Atmospheric and Climate Science Directorate

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Pathways to the Arctic – The Grasshopper Effect

The Atmospheric Heavy Metals (GRAHM) Model

How can pesticides and other pollutants that are used in far off places like India or Africa end up in the Canadian Arctic, and in concentrations high enough to be harmful to plants, animals and people so far away from the source regions? Canadian scientists have been working to solve this puzzle for many years and have made great progress in understanding the overall picture of how toxic substances end up in Arctic ecosystems.

Two major processes are at work here. First, is the atmospheric transport of pollutants from source regions to the Arctic. Although this has been accepted on a theoretical basis, scientists at the Meteorological Service of Canada MSC have developed a model to simulate these transport processes. This global numerical model simulates emissions of specific pollutants, such as pesticides and mercury, and shows how they move around the globe, and are influenced by daily variations of weather patterns.

This powerful model, called the Global/Regional Atmospheric Heavy Metals model (GRAHM) showed that a major pathway for these pollutants on their journey to Canada passes right over the Canadian Arctic. This starts to explain why atmospheric levels of these toxic pollutants in the Arctic are similar to those in southern Canada.

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GRAHM model output for January 9, 1997, showing the surface air concentrations of total gaseous mercury (in nanograms/m3) in the Northern Hemisphere. The figure gives an indication of the pathway for the transport of mercury into the Canadian arctic.

The second process influencing pollutant transport to the Arctic is global distillation due to temperature differences in the atmosphere that cause evaporation and condensation of pollutants. This global distillation process is also known as the “grasshopper effect”. Mercury and many pesticides behave differently at different temperatures. At high temperatures, they evaporate into the atmosphere, but at low temperatures they condense out of the atmosphere and are deposited onto land surfaces, lakes and forests. As temperatures change from day to night and from winter to summer, these pollutants are repeatedly evaporated and condensed. Slowly but surely, the pollutants make their way northward.

Once in the northern ecosystems, these pollutants bio-accumulate in plant and animal tissues where their toxic effects are magnified up through the food chain, reaching harmful levels in both humans and animals.

Scientists now have a better understanding of how pesticides that are meant to improve productivity in one part of the world can have an unintended and adverse consequence on the other side of the globe in the Canadian Arctic.

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Gaseous atmospheric mercury concentrations at Alert, Nunavut (1995-2001). Mercury concentrations tend to be fairly uniform across rural Canada, but fall dramatically at polar sunrise in the high Arctic as shown in this figure.

“The GRAHM model is proving to be a valuable tool in tracking the long range transport of mercury, particularly over the Arctic. The model is contributing to the Arctic Monitoring and Assessment Program (AMAP) Assessment of Heavy Metals, which is underway. ”
Lars-Otto Reiersen
Executive Secretary
Arctic Monitoring and Assessment Program

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