What Is Ozone?

Ozone is a highly reactive molecule consisting of three oxygen atoms. Ozone occurs throughout the troposphere, which is the lowest layer of the atmosphere. Ozone is only a problem at ground level. In the upper atmosphere, an ozone layer helps shield the earth from harmful ultraviolet radiation.

Small amounts of ground-level ozone have always been present and are naturally produced from soil emissions, thunderstorms and forest fires. Human activities, however, create enough additional ground-level ozone to be a hazard to health and to damage plants and buildings. Ozone causes the most serious health problems for young children, some elderly people, and people with lung conditions such as asthma.

See the next page for common sources of air pollution.