What is Ozone (Ground-Level Ozone, or “Smog”)?
Ozone is a colorless gas that can be found throughout the earth’s atmosphere. In the upper atmosphere, ozone exists naturally where it shields the earth from the sun’s ultraviolet rays. At ground-level, however, ozone is formed as a result of chemical reactions caused by the presence of nitrogen oxides (NOx) and volatile organic compounds (VOCs). These compounds react with oxygen in the air in the presence of heat and strong sunlight to produce ground-level ozone, the primary ingredient of summertime smog. Ground-level ozone is one of the six criteria air pollutants (see “Related Programs”) identified by the US Environmental Protection Agency under the federal Clean Air Act. Because of the health effects and the widespread nature of ground-level ozone, it has been a major focus of air quality regulatory agencies across the country. These efforts have included ambient air quality monitoring and providing air quality forecasts to inform the public when ozone levels are anticipated to be
