Ozone is formed during a photochemical reaction, meaning several common airborne pollutants react with sunlight to form another pollutant called ozone. Ideal conditions for ozone formation require warm, windless days with bright sunlight found during the summer and early fall.

During these conditions, volatile organic compounds (VOCs) react with nitrogen oxides (NOx), also called “ozone precursors” to form ozone. Volatile organic fumes come from evaporation of gasoline, paint, solvents, consumer products, varnishes, and industry chemicals.

VOCs + NOx + Heat + Sunlight = Ozone

Nitrogen oxides come from high-temperature combustion found in exhaust from auto and truck engines, boilers, utilities and other sources. The concentration of these precursor gases, the volume of air to dilute and mix, the temperature and intensity of ultraviolet light affect this process.

Both urban and rural areas of the state are subject to elevated ozone levels as winds carry emissions hundreds of miles away from their original sources.

• Iowa's Sources of Ozone Precursors
• Ozone: Good Up High, Bad Nearby
• Human Health and Environmental Effects of Ground-level Ozone
• What Communities can do to Reduce Ozone Precursors
• What You Can Do to Reduce Ozone Formation