Background Story

The sun’s radiation reaches the Earth’s atmosphere in several different wavelenths, broken up by ranges of specific lengths (measured in nanometers).  The three ranges of wavelenths most relevant to biological systems are Photosynthetically Active Radiation (PAR), UV-A (320-400 nm), and shorter UV-B (280-320 nm).

Ozone depletion in the stratosphere

Above is a diagram that shows the process by which ozone (O3) is depleted in the stratosphere, allowing UV-B light that is usually screened by O3 from hitting the surface of the Earth.  Naturally, a small amount of UV-B does get through the layer of ozone in the stratosphere, which living beings are adapted to exposing at these minimal levels. However, too much UV-B can be damaging to cells…this is why there has also been a concern over the last few decades about humans being vulnerable to skin cancer due to this type of radiation.

The layer of ozone existing above the Earth starts to disappear because of a series of chemical reactions that take place when CFC’s enter the atmosphere. CFC’s are aerosols that get released by human use of products such as refrigerants and hairsprays, and move up through the atmosphere eventually reaching the layer called the stratosphere.  When the elements in chloroflourocarbons interact with ice particles, present across many parts of the globe at various times of the year but especially in the clouds floating over Antarctica during austral spring, these compounds are broken apart leaving free chlorine ions. The chlorine ions are then free to attach to ozone particles, which in turn breaks those O3’s that make up the ozone layer into ClO and O2. Below are the specific chemical reactions just described:

Cl + O3 => ClO + O2

O3 + hv (sunlight) => O + O2


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