International Day for the Preservation of the Ozone Layer – Ozone Fact Sheet


Today is being observed as International Day for the Preservation of the Ozone Layer. This year marks the 30th anniversary of the Vienna Convention for the Protection of the Ozone Layer, an important milestone in the protection of the ozone layer. The theme is “30 Years of Healing the Ozone Together,” supported by the slogan “Ozone: All there is between you and UV.”

The ozone layer is a fragile shield of gas that protects the Earth from the harmful ultraviolet rays of the sun, helping preserve life on the planet. According to the US-based Environmental Protection Agency (EPA), “less protection from ultraviolet light will, over time, lead to higher skin cancer and cataract rates and crop damage. The US, in cooperation with 190 other countries, is phasing out the production of ozone-depleting substances in an effort to safeguard the ozone layer.” Here are some more facts:

  1. Ozone is mainly found in two regions of the Earth’s atmosphere. The stratosphere, which begins between six and 10 miles (10 and 17 kilometers) above the Earth’s surface and extends up to about 30 miles (50 kilometers), contains about 90 per cent. This is what is commonly known as the ozone layer. The remaining ozone is found in the lower region of the atmosphere, called the troposphere.
  2. Stratospheric ozone absorbs most of the biologically damaging ultraviolet sunlight, allowing only a small amount to reach the Earth’s surface, which is why it’s called ‘good ozone.’ On the other hand, tropospheric ozone is considered ‘bad ozone’ because it reacts strongly with other molecules, creating conditions that are toxic to living systems. Several studies have shown the harmful effects of ozone on crop production, forest growth, and human health.
  3. Ozone is very rare. In the Earth’s atmosphere, it averages only about three molecules to every 10 million air molecules.
  4. Although we say “hole in the ozone layer” or “ozone hole,” there’s no actual hole.  Instead, the protective layer contains less good ozone than it used to.  This thinning is found all over the earth, but the biggest losses are over the North and South Poles. That’s because ozone destruction is worse when it’s very cold.
  5. Chlorofluorocarbons (CFCs) have been found to contribute significantly to ozone depletion. CFCs, which contain chlorine, can only be broken down with exposure to strong UV radiation. When that happens, the CFC molecule releases atomic chlorine. One atom of this chlorine can destroy more than 100,000 ozone molecules. The net effect is to destroy ozone faster than it is naturally created.

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