A major agent in the formation of air pollution, this is actually a form of oxygen. Ozone is a result of photochemical reactions involving emissions from automobile and industrial processes. Ozone does occur naturally in earth's upper atmosphere (the ozone layer) where it protects the earth's surface against harmful effects of the sun's radiation. Ozone accumulation close to the earth's surface is harmful. Ozone depletion in the upper atmosphere is also harmful, as the ozone layer is essential to the preservation of the earth.