Ozone depletion

Scientists discovered in the 1970s that the ozone layer was being depleted.

Atmospheric concentrations of ozone vary naturally depending on temperature, weather, latitude and altitude, while substances ejected by natural events such as volcanic eruptions can also affect ozone levels.

However, these natural phenomena could not explain the levels of depletion observed and scientific evidence revealed that certain man-made chemicals were the cause. These ozone-depleting substances were mostly introduced in the 1970s in a wide range of industrial and consumer applications, mainly refrigerators, air conditioners and fire extinguishers.

If ozone molecules are depleted faster than natural production, the result is an ozone deficit. The depletion of the ozone layer leads to a reduction in its shielding capacity and thus greater exposure of the earth’s surface to harmful UV-B radiation. UV radiation is categorized into three types; UV-A, UV-B and UV-C. UV-C does not reach the earth’s surface. UV-B is partially filtered by the ozone layer. And UV-A is not filtered at all by the ozone layer Ozone depletion is caused by the release of certain chemicals into the atmosphere.

Release of manmade chemicals such as halogenated hydrocarbons to atmosphere disturb the natural equilibrium of forming and destroying ozone molecules.  If the destroyed ozone molecules are not replaced quickly enough by the new ozone molecules, the equilibrium will be out of balance and the concentration of ozone molecules will be reduced. Even after one ozone molecule is destroyed, the ODS are still be available to destroy even more ozone molecules. Because the destructive lifetime of ODS may range from 100 to 400 years, depending on the type, one molecule of ODS could destroy hundreds of thousands of ozone molecules.

Figure: Illustration ozone depletion process with chlorofluorocarbons (CFCs) Source: UNEP (2013)