Fact sheets

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The Ozone layer

What is the Ozone Layer?

Ozone (O₃) is a colourless gas that is a chemical cousin of molecular oxygen (O₂). Most of the ozone in the atmosphere is found in a layer between 15 and 35 km above the earth's surface in a region of the atmosphere known as the stratosphere. The ozone layer is beneficial to life on earth as it absorbs the harmful ultraviolet (UV) radiation from the sun. In contrast, ozone at ground level, although it also absorbs some UV, can be harmful to living organisms. Most ozone at ground level is formed as urban air pollutants mix together on hot summer days. This ozone is one of the principal components of smog, and can be a serious health concern.

What is happening to Canada's ozone layer?

Over southern Canada, the ozone layer has thinned by an average of about 6% since the late 1970s. The largest depletions over southern Canada occur during the spring months, where ozone thinning averages about 8% to 10%, and may reach 20% for short periods. Ozone depletion is most severe in the high Arctic during the early spring, where reductions of up to 45% have been recorded in recent years.

The earth's atmosphere

Near ground level, ozone is a serious air pollutant. In the stratosphere, it forms the ozone layer - the earth's protective sunscreen.

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