In nature, there is a cycle of oxygen just like there is a cycle of water. Oxygen is released from plants on land and plankton in the sea during photosynthesis. The oxygen is lighter than air and floats upward in the atmosphere. The ozone created exists as a thin layer in the atmosphere and it blocks out the small portion of the UV spectrum that it absorbs.
Ozone is produced constantly in the upper atmosphere as long as the sun is shining.
Since ozone is heavier than air, it begins to fall earthward. If ozone contacts water vapor as it falls, it forms hydrogen peroxide, a component of rainwater, and the reason why rainwater causes plants to grow better than irrigation. Ozone is also created by lightning, and the amount produced in an average storm is often triple the allowable limit of 0.15 ppm as set by the U.S.A. Environmental Protection Agency. This ozone is what gives the air the wonderful fresh smell after a rain, and is of the highest benefit to anyone fortunate enough to be breathing it. Another way ozone is produced is by photons from the sun breaking apart nitric oxide, a pollutant formed by the combustion of hydrocarbons in the internal combustion engine.