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What Caused the Hole in the Ozone Layer

The ozone layer is a layer made up of a high concentration of ozone (O3) located in the stratosphere, which is the second major layer of Earth’s atmosphere. The ozone layer is known to absorb 97-99% of the high frequency ultraviolet (UV) light from the sun. This means that this layer is extremely important because it protects life on Earth from the harmful UV radiation. The ozone layer was discovered in 1913 by Charles Fabry and Henri Buisson and was studied further by G. M. B. Dobson who created a network of monitoring stations. The discovery of a large ozone hole in the Antarctic was announced in 1985 by scientists Joe Farman, Brian Gardiner and Jon Shanklin. Although ozone holes had been hypothesized much earlier, it came as a surprise because it was much larger than had been predicted. If you want to know what causes holes in the ozone layer, keep reading to find out.

What causes holes in the ozone layer?
The cause of ozone layer depletion was hypothesized in the 1950’s when David Bates and Marcel Nicolet showed that some free radicals, particularly hydroxyl and nitric oxide, could reduce the amount of ozone. In 1970 Paul Crutzen showed that nitrous oxide emissions effects the levels of nitric oxide in the atmosphere. In 1974 Frank Sherwood Rowland and Mario J. Molina furthered this research by suggesting that organic halogen compounds, such as chlorofluorocarbon (CFS), were capable of reaching the stratosphere and that they would be broken down by ultraviolet radiation releasing a chlorine atom. Chlorine was already known to be more efficient at destroying ozone than any other substance. Crutzen, Rowland and Molina were awarded the Nobel Prize in Chemistry in 1995.

This research caused much controversy, but it was later shown that the man-man compounds chlorofluorocarbons (CFC’s) and bromofluorocarbons were stable enough to reach the stratosphere where they were broken down by the ultraviolet light and Cl or Br atoms were released. These free radicals then break down the ozone, which caused the holes to form in the ozone layer. On September 16, 1987, the Montreal Protocol was created to phase out the use of halogenated hydrocarbons that contain chlorine or bromine. If CFC’s had not been banned it is estimated that 30-50% of the ozone layer would have been depleted by 2050!

Did you know?
CFC’s were invented in the 1920’s by Thomas Midgley, Jr. and were widely used in air conditioning and aerosol sprays prior to the Montreal Protocol.

It is estimated that one CFC molecule can last in the upper atmosphere for about 100 years and destroy about 100,000 ozone molecules during this time!

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