Ozone is a molecule that serves both good and bad functions.
In the lower atmosphere, the troposphere, ozone is a major component of smog. It is created when sunlight reacts with hydrocarbons and nitrogen oxides that are emitted by automobiles, auto body shops, gas stations, organic solvents and dozens of other sources. The concentration of ozone in the air also strongly correlates to many meteorological characteristics including temperature, wind speed and atmospheric stability. Ground level ozone should not be confused with the protective ozone layer in the upper atmosphere, the stratosphere, that shields the Earth from the harmful ultraviolet rays of the sun. It is important that people do not mistake one for the other.