What it is and Where it Comes From

Image depicting the formation of ozone in the atmosphere (VOCs + NOx + Heat + Sunlight = Ozone)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.

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.

EPA's Ozone, good up high, bad nearby graphicGood Up High, Bad Nearby

Ozone occurs in two layers of the atmosphere. The layer closest to the Earth’s surface is the troposphere. Here, ground-level or “bad” ozone is an air pollutant that is harmful to breathe and it damages crops, trees and other vegetation.

Six miles up is the second layer of atmosphere called the stratosphere. The stratosphere or “good” ozone layer extends upward from about 6 to 30 miles and protects life on Earth from the sun’s harmful ultraviolet (UV) rays.

Ozone loss in the stratosphere can cause increased amounts of UV radiation to reach the Earth which can lead to increased cases of skin cancer, cataracts, and impaired immune systems. Overexposure to UV is believed to contribute to the increase in melanoma, the most fatal of all skin cancers. Since 1990, the risk of developing melanoma has more than doubled. UV can also damage sensitive crops, such as soybeans, and reduce crop yields.