When ozone is produced on the ground from cars and factories, it is harmful and forms smog. Pollutant such as chlorofluorocarbons (CFC’s) from factories, refrigerators, and air conditioners rise through the atmosphere. The chlorine in the CFC molecule attacks the ozone molecule destroying it. When the molecules in the ozone layer are broken apart (from above by the sun and below by pollution), the layer is thinned allowing more harmful UV rays to reach the earth.
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Thin areas in the ozone layer are sometimes called holes. The ozone layer is thinnest over the equator, the poles, and major metropolitan areas (cities). If left alone the ozone layer will spread out and fill in the thin spots.