What is Ozone?

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 perhaps the most widespread and damaging of the six criteria air pollutants identified by the U.S. Environmental Protection Agency under the federal Clean Air Act.

As the major ingredient in summertime smog, ozone has strong oxidizing properties that irritate, and in some cases, damage lungs, throat, and eyes. Ozone can limit the ability to take a deep breath, and it can cause coughing, throat irritation, and breathing discomfort. Children and those with pre-existing lung problems, such as asthma, are more sensitive to the harmful effects of ozone. Even healthy adults involved in moderate or strenuous outdoor activities can experience the unhealthy effects of ozone exposure. An Air Quality Action Day is called in New Hampshire when ozone is forecast to reach unhealthy levels. During an Air Quality Action Day, people are encouraged to take precautionary measures to protect their health, especially in the afternoon when ozone levels tend to be the highest.

Ozone also inhibits foliage growth and can severely reduce its ability to reproduce, often leaving plant life weakened and susceptible to insect infestation and cold weather damage.

Sources of VOCs and NOx emissions are many and varied. Almost all NOx emissions originate from human activities and are formed from fossil fuel combustion, principally from power plants, industrial boilers, and cars and trucks. Conversely, over 85 percent of VOC emissions in New Hampshire result primarily from forests and other vegetation. Other VOC sources include cars and trucks, solvents and paints, storage and distribution of gasoline, and manufacturing facilities.