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Understanding the effects of atmospheric sulfate
At the University of Calgary, Dr. Ann-Lise Norman is investigating the complex relationship between gases, particles, clouds and precipitation, in hopes of using this knowledge to more accurately predict extreme precipitation events.
“Cloud formation, persistence and extent, as well as precipitation formation is thought to be related to particles that may form from pollutants and marine biogenic emissions,” she says. “Ultimately, clarifying the role these processes play with respect to clouds and precipitation will help improve regional and local climate predictions.”
A professor in the Department of Physics and Astronomy, Dr. Norman’s current project aims to contrast the effects of marine biogenic emissions versus pollutants in marine air. She and her team are using GEOS-Chem, a global 3D chemical transport model for atmospheric composition, to compare global and local emissions of aerosol sulfate to those recorded at Saturna Island (pictured above), located east of Vancouver in the Strait of Georgia. They chose Saturna Island, she says, because weekly aerosol, SO2, and precipitation samples collected by Environment Canada are shipped to Calgary for isotope apportionment studies. These provide "ground-truth" measurements against which the model output was compared.
“Access to WG was essential for this research as we had large input and output files,” she adds. “In this study we nested a smaller North American grid (0.5 x 0.625 degrees) within a coarser global grid (4 x 5 degrees) and used the NASA Global Modelling Assimilation Office (GMAO) meteorology to compare the spatial and temporal data from the model with measurements in the Greater Vancouver region and Saturna Island using sulfur isotope source apportionment.”
The pie chart to the right shows some of the results from their modelling work, which identifies three main contributions to atmospheric sulfate at Saturna Island:
- global ship emissions (ARCTAS),
- dimethyl sulphide oxidation (marine biogenic: DMS), and
- anthropogenic emissions from the area (2005 inventory: NEI).
“The very good agreement between the measurements and model for sulfate apportionment in the Greater Vancouver region suggests the emissions inventory and model output is well constrained,” she says.
Without having WestGrid and Compute Canada's computational resources, Dr. Norman and her team would not have been able to create these models or analyze them.
“Access to WestGrid computational and support help was instrumental in obtaining our results,” she says.
As a followup to this study, Dr. Norman says she would like to apply the GEOS-Chem model to compare its outputs to apportionment studies based on measurements in areas of Alberta, off the coast of Newfoundland, and in parts of the Arctic.