Ozone is the primary ingredient of smog in our cities and other areas of the country.
Though it occurs naturally in the stratosphere to provide a protective layer high above the earth, at ground-level it is the prime ingredient of smog. Ground-level ozone is formed when volatile organic compounds and nitrogen oxides react in the presence of sunlight. Sources of volatile organic compounds and nitrogen oxides include automobiles, power plants, gas stations, paints, cleaners, aircraft, locomotives, and lawn and garden equipment. Ozone concentrations can reach unhealthy levels when the weather is hot and sunny. While beneficial in the upper atmosphere, ozone in the lower atmosphere can cause a variety of health problems because it damages lung tissue, reduces lung function, and adversely sensitizes the lungs to other irritants.