Ozone is a gas that consists of three atoms of oxygen.
It can be both beneficial and harmful, depending on where it is located in the atmosphere. Ground level ozone, however, is a pollutant which can be harmful to people, plants and various materials. Ozone is not emitted directly by any source. Smog Alert days are announced via the news media, highway message signs and the internet. The announcements remind metro Atlantans to use their automobiles less and take other steps to reduce ozone.