There are two different types of ozone depletion, both are very similar. The first one has been a slow, but steady ozone depletion of 4% per decade of the Earth’s stratosphere(ozone layer). This has been happening constantly since the 1970’s. The other is a much larger, although seasonal loss of ozone over the polar regions. This yearly occurrence is called the ozone hole. There are many causes for ozone depletion, but the most important process in both trends is catalytic destruction of ozone by atomic chlorine and bromine. Both come from the breaking down of chloroflourocarbons(freons) by photons in the atmosphere.