Atmospheric and Climate Science Directorate

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The Effectiveness of the Montreal Protocol on Ozone Depleting Substances

Systematic Measurements of Stratospheric Ozone & UV

Since 1987, 183 countries have ratified the United Nations Montreal Protocol that limits the emissions of ozone-depleting substances. To determine the effectiveness of the Protocol, the World Meteorological Organization (WMO) established a global network to monitor solar UV radiation and changes in the ozone layer. The Meteorological Service of Canada MSC has a network of 12 stations across Canada that measure column ozone and UV-B.

The Canadian ozonesonde network consists of six stations that launch ozonesonde carrying balloons weekly to determine long-term trends of ozone concentrations at all levels of the atmosphere.

MSC scientists have been leaders in this field for nearly 50 years. In the mid-1970's, they directed their expertise in high precision measurements of the sun's energy into the development of the Brewer spectrophotometer, an instrument that measures column ozone and UV-B. This instrument has become the standard for ground-based measurements around the world. It is now manufactured under licence, and over 160 instruments are used in more than 40 countries worldwide, plus Antarctica. MSC maintains the world standard calibration group of instruments at its headquarters in Toronto, and operates the World Ozone and UV Radiation Data Centre as part of Canada's commitment to the WMO. Examples of ozone and UV data include forecast maps used to predict the UV index for Canadians, and near-real time ozone measurements and maps from groundbased instruments and satellites.

Ozone depletion is most severe at the Earth's poles. The Antarctic ozone hole is well documented, and a significant thinning of the ozone layer over the Arctic was first detected in the measurements from Eureka, Alert and Resolute in Canada's high Arctic. This ozone depletion over the Arctic has been linked to climate change. Climate models predict that as the surface warms, the stratosphere cools and ozone destruction is accelerated. In 1993, MSC researchers were the first to definitively link an increase in mid-latitude UV-B at the Earth's surface to depletions of ozone in the stratosphere. This was particularly significant in that it showed that ozone depletion was not only a problem in Polar Regions. Canada also measures the vertical distribution of ozone using a small instrument package called an ozonesonde that is carried aloft by weather balloons. This information is important in understanding ozone depletion chemistry and global ozone transport. Three of the six Canadian stations involved in this program are in the high Arctic. The knowledge gained from this program, along with that from the other monitoring networks, is critical to our ability to monitor the recovery of the ozone layer.

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Global monthly means of the major CFCs and halons as parts per trillion (ppt) in the atmosphere versus time from the NOAA Climate Monitoring and Diagnostics Laboratory (CMDL).The means include measurements from Alert, NT; Pt. Barrow, Alaska; Niwot Ridge, Colorado; Mauna Loa, Hawaii; American Samoa; Cape Grim,Tasmania, and the South Pole.

The expertise of MSC researchers and the location of Canadian monitoring stations have enabled Canada to make a unique contribution in this area of science, and to work together with the international community in tracking the effectiveness of international environmental management policy.

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Long term vertical ozone distributions over the Canadian Arctic from 1966-2000 with the annual average for 1966- 1997 subtracted from the data to show concentration deviations from normal. The green and blue areas indicate lower than normal ozone concentrations, and are evident in the recent years (1993, 1995, 1996, 1997, 2000, 2003). These major losses occur in the late winter - early spring. (The data are in Dobsin Units (DU) per km which is equivalent to 0.01 mm thickness at standard temperature and pressure.)

"MSC's research & development is making a strong contribution to international efforts to elucidate the coupling between stratospheric ozone depletion/recovery and climate change.”
International Independent Peer Review 2001

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