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Ozone layer over Canada
The Ozone Layer Over Mid-Latitudes in Canada
The ozone layer over Canada is located in the stratosphere from approximately 10km to 50km above the Earth's surface. The amount of ozone over any location varies from day to day as the meteorological conditions change in the stratosphere. This natural variation can be up to 30 percent of the total column ozone. As shown in the graphs below, the ozone layer is thickest over Canada during the late winter and spring while it is thinnest during the early fall. This is due to breakdown of ozone by the UVB radiation in sunshine during the summertime when the natural destruction of ozone exceeds the production of ozone in the upper reaches of the stratosphere.
Toronto, Ontario in 2002
Churchill, Manitoba in 2002
Other locations are available at: ftp://exp-studies.tor.ec.gc.ca/pub/giffiles/o3_graphs/
Arctic
The amount of total ozone over the Arctic reaches a maximum during February and March. At this time of the year because of the lack of sunshine to break ozone down, the concentration of ozone over the Arctic increases. The destruction of ozone in the Arctic stratosphere is dependent on temperature. When the temperatures falls into the -80C range polar stratospheric clouds will form. These clouds act as a catalysis in converting stable pollutant compounds such as CFCs into reactive compounds that will destroy ozone in the presence of sunlight. This will happen in the month of March as the sunshine returns to the North resulting in large deviations from normal values as seen in the graphics below.
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1982
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1986
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1990
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1994
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1998
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2002
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The worst years for ozone depletion:
In 2003, the Arctic ozone layer was not characterized by extensive and severe ozone depletion. There was, however, an area from Alert to Siberia where depletion was between 20-35%.
Ozone Depletion
Since 1982, the ozone layer has been thinner especially in the southern hemisphere as the two graphs below illustrate. In the Northern hemisphere over mid-latitudes, the ozone layer was the thinnest in 1993 when aerosols from the Pinitoba volcano combined with high concentrations of manmade ozone-depleting substances reduced the ozone layer by 7%. Since that time, the ozone layer has recovered somewhat to about 4% below the pre-1980 averages. In the Southern Hemisphere, the ozone layer began to become thinner in 1980 and continued throughout the years reaching about 7% below the long-term pre1980 averages in 2001.
Ozone-depleting Chemicals in the Atmosphere
The graph below from the Climate Monitoring and Diagnostic Laboratory of NOAA
(www.cmdl.noaa.gov/hats/graphs/graphs.html) shows that the concentration of ozone-depleting substances (ODS) with short life times have started to decrease or level off in in the lower atmosphere. These include CFC-11 (chlorofluorocarbon), CFC-113, CH3CCl3 (methyl chloroform), and CCl4 ( carbon tetrachloride). Other ODSs with a long lifetime are still increasing in concentration in the lower atmosphere. These include the replacement gases such as HCFC-14b and HCFC-142b (hydro chlorofluorocarbon) as well as halons. Overall, the total equivalent ODS in the lower atmosphere is decreasing. It was expected, however, that it would take an additional 5 years for this trend to start in the stratosphere.
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Created :
1999-04-01
Modified :
2002-12-18
Reviewed :
2002-12-18
Url of this page : http://www.msc.ec.gc.ca
/education/uvindex/science/ozone_layer_over_canada_e.html
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Environment Canada's World Wide Web Site.
