About atmospheric gases and ozone

SCISAT studies the complex chemical reactions occurring in the middle atmosphere that affect ozone. Ozone shields the surface of the Earth from a large percentage of the Sun's harmful ultraviolet rays. Keeping the ozone layer healthy is essential for sustaining life on Earth.

To measure the concentration and identify some 30 to 35 molecules in the Earth's atmosphere, such as ozone, nitric acid, and hydrochloric acid, SCISAT uses the light of the Sun. Each molecule has a colour or wavelength by which it can be identified. The amount of sunlight absorbed shows its concentration.

Ozone depletion and seasonal variation

Certain compounds are known to deplete ozone in the stratosphere, such as chlorofluorocarbons (CFCs), halons, carbon tetrachloride, and methyl chloroform. The international agreement to stop the production of these compounds is the Montreal Protocol on Substances that Deplete the Ozone Layer.

Despite actions taken to protect the ozone layer, severe depletion is occurring in the Arctic during the late winter and early spring, making Canada vulnerable to the effects of a weakened ozone layer.

Ozone layer measurements vary depending on the day, the season and the year. For example, above Resolute in Nunavut, daily measurements can fluctuate anywhere between 10 and 25%.

During the dark polar winter, unstable atmospheric conditions cause chemical reactions that don't take place anywhere else on Earth. As daylight returns to the North in the spring, ultravilolet light from the Sun causes the release of ozone-depleting molecules. When the seasons change again, the dynamic reverses.

Measuring ozone

The ability to measure ozone in the atmosphere was developed by G.M.B. Dobson who built the first spectrograph in 1924. The Dobson Unit is the most common unit for measuring ozone concentration. It describes how much ozone there would be in a column cross-section of the atmosphere if it were all squeezed into a single layer.

Canada has a network of ozone monitoring stations. Each houses a Brewer Ozone Spectrophotometer, an instrument developed and operated by Environment Canada. Records of the ozone layer over Canada go back more than three decades. Early accounts are vital to understanding the changes occurring today.

The main advantage of satellite data over data obtained from the ground is that we can obtain coverage of the far North. A global perspective on ozone is important in understanding the vulnerability of this region.