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LEARN MORE: Tracking Ozone

There are several factors involved with the formation of ground level ozone, including:

  • Sunlight/Ultraviolet Radiation: Ground level ozone is produced by a photochemical reaction. A photochemical reaction is a chemical reaction that requires light (in this case sunlight) to provide the energy for the reaction to proceed. During the summer months, the earth is tilted in such a way that the sun's rays are more direct, and more intense. This combination creates longer and warmer days than in the winter months. Ground level ozone is called the "summertime pollutant" because that is the time of year when the energy from the sun is intense enough to trigger the photochemical reaction necessary to produce ground level ozone from NOx and VOCs.
  • Cloud Cover: Cloudless skies create conditions for warmer days to occur. But keep in mind that a completely cloudless sky is not necessary for the photochemical process to start.  The more sunlight available, the more likely the ground level ozone photochemical reaction will occur.
  • Temperature: High temperatures can increase ozone levels by increasing the rate at which the chemical reaction described above occurs.
  • Wind Direction: NOx can travel large distances before reacting to form ozone. For that reason, it creates regional pollution problems, rather than simply affecting the local area where it is emitted. The action of pollutants traveling distances is called transport. Transported pollutants contribute significantly to the presence of ground level ozone in rural areas.
  • Wind Speed: Low wind speeds (less than about 10 mph) are necessary for the accumulation of pollutants and subsequent formation of high concentrations of ozone. At speeds above about 10 mph, pollutants are diluted too rapidly for ozone to accumulate significantly.
  • Volatile Organic Compounds (VOC's): Emissions from human activities include driving, industrial manufacturing, lawn mowing and painting are all sources of hydrocarbons. VOC's are one of the necessary ingredients to the ozone equation.
  • Oxides of Nitrogen (NOx): Nitrogen oxides (NOx), the other chemical precursor of ozone, are produced whenever fossil fuels are burned and are primarily produced by motor vehicles and power plants.

The photochemical reaction that produces ground level ozone requires several factors to be present and tends to occur when a stagnant air mass develops during hot and sunny conditions. The air will not become stagnant if weather systems continue to move through the area and displace the air with cleaner, "fresher" air.


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