Unlike many air pollutants which are emitted directly from a specific source, such as sulfur dioxide from a power plant, ozone is a regional pollutant and is created in a series of complex chemical interactions in the atmosphere. Nitrogen oxides from burning automobile fuel and hydrocarbons from other petroleum based fuels or natural sources, react in the presence of sunlight and high temperatures, to create ozone. This pollutant can drift with polluted air masses several hundred miles from source areas, causing a regional problem.
Ozone is a major component of urban smog.
In humans, ozone can lower resistance to diseases such as colds and pneumonia, damage lung tissue, intensify heart and lung disease, and cause coughing and throat irritations. Even healthy adults who perform heavy physical exercise or manual labor outdoors experience the unhealthful effects of ozone. Each molecule of ozone is composed of three atoms of oxygen, one more than the oxygen molecule which we need to breathe to sustain life. The additional oxygen atom makes ozone extremely reactive. Ozone exists naturally in the earth's upper atmosphere, the stratosphere, where it shields the earth from the sun's ultraviolet rays.