Altitude UV intensity increases with altitude because there is less atmosphere to absorb the damaging rays. Weather Conditions Cloud cover reduces UV levels, but not completely. Depending on the thickness of the cloud cover, it is possible to burn on a cloudy summer day even if it doesn't feel very warm. In the 1980s, scientists began accumulating evidence that the ozone layer was being depleted. US Ozone is a naturally occurring gas found in the earth's atmosphere that absorbs certain wavelengths of the sun's UV radiation.
Ozone is concentrated in a part of the atmosphere called the stratosphere.
Stratospheric ozone is most concentrated between 6-30 miles above the earth's surface. Ozone is also broken apart as it absorbs UV radiation. In this way, UV helps sustain the natural balance of ozone in the stratosphere, while ozone in turn absorbs UV, protecting life on earth from harmful radiation. They migrate into the upper atmosphere after use. Because they are heavier than air, they have to be carried by air currents into the stratosphere, a process that can take as long as 5 to 10 years.