Ozone is mainly found in two regions of the Earth's atmosphere. The remaining ozone is in the lower region of the atmosphere, the troposphere, which extends from the Earth's surface up to about 10 kilometers. The figure below shows this distribution of ozone in the atmosphere. The ozone molecules in these two regions are chemically identical, because they all consist of three oxygen atoms and have the chemical formula O 3 . However, they have very different effects on humans and other living beings.
Ozone thus plays a key role in the temperature structure of the Earth's atmosphere.
Without the filtering action of the ozone layer, more of the Sun's UV-B radiation would penetrate the atmosphere and would reach the Earth's surface. Many experimental studies of plants and animals and clinical studies of humans have shown the harmful effects of excessive exposure to UV-B radiation. At the Earth's surface, ozone comes into direct contact with life-forms and displays its destructive side. Because ozone reacts strongly with other molecules, high levels of ozone are toxic to living systems. Several studies have documented the harmful effects of ozone on crop production, forest growth, and human health.