OZONE
The ozone layer is located about 30 to 100 Km above the earth. The level of the ozone layer varies according to location and time of year. There is for instance, generally more ozone as you move away from the tropics and more in the winter and spring than in the fall and summer.
The ozone layer filters out much of the UVB but has relatively little affect on UVA. It is UVB therefore that will be most affected by any change in atmospheric ozone.
Unfortunately, the ozone layer is delicate. The use of Chloroflourocarbons (CFCs) has severely damage the ozone layer. CFCs are released by the use of air conditioners, aerosols, sprays and certain solvents. CFCs released now take about 7 years to get to the ozone layer and do their damage. The average CFC "life span" is about 100 years which means that even after we stop using them, they will be damaging the ozone layer for a long time to come. On the bright side, CFC emissions have decreased drastically over the past few years mostly do the "Montreal Protocol" : a protocol ratified in 1987 and signed by most of the industrialized nations that calls for a 50% reduction in CFC production from 1986 levels by the year 1999.
