It seeks to bind with any substance amenable to oxidation. Ozone's reactivity makes it harmful. It is one of the principal components of urban smog. Oxygenated fuels are used exclusively in most urban areas in the winter to keep it from forming. Incomplete burning of fossil fuels is the primary source man made ozone.
Ozone exists at all levels of the atmosphere.
It is slightly concentrated at upper levels. Ozone is created in this zone by a natural process, a reaction between sunlight and stratospheric oxygen. Levels fluctuate naturally, depending on the output of the sun and its angle of intensity. When the sun returns the following spring, the level rebuilds. Ozone does absorb some ultraviolet radiation, and excessive ultraviolet radiation can be harmful.