Ozone (O3) is an extremely reactive gas molecule composed of three oxygen atoms. Ozone forms in chemical reactions in the atmosphere when nitrogen oxides (NOx) and volatile organic compounds (VOCs), also called hydrocarbons, come into contact with both sunlight and heat.
VOCs and NOx form when fossil fuels like gasoline or coal burn or when fossil fuel-based chemicals, like paints, evaporate. NOx is emitted from power plants, motor vehicles and other sources of high-heat combustion. VOCs are emitted from motor vehicles, chemical plants, refineries, factories, gas stations, paint and other sources.
When and where is ozone a problem?
Ozone levels typically rise in much of the nation between May and October due to a combination of higher temperatures, more sunlight, and stagnant air masses. However, some parts of the nation have unhealthful levels independent of the season.1
Unhealthful levels of ozone show up all across the nation, based on current scientific understanding of health risks. Wind patterns blow ozone produced in one region into other regions.
