Ozone (O3)

Contact: Air Quality Related Issues: Erica Wolf, 517-284-6766
Agency: Environmental Quality

Ozone is a highly reactive gas that consists of three oxygen atoms: one with a double bond and the other with a single bond. It has the same chemical structure whether it occurs miles above the earth or at ground level. Depending on its location in the atmosphere, ozone is considered either good or bad.

Good ozone occurs naturally in the stratosphere approximately 10 to 30 miles above the earth's surface and forms a layer that protects life on earth from the sun's harmful rays. The common phrase "hole in the ozone" refers to the ozone in this layer. Various refrigerants contain chlorofluorocarbons or hydrochlorofluorocarbons. Once released, they migrate into the upper atmosphere where a complex series of chemical reactions occur destroying ozone molecules and thinning the protective ozone layer.

In the earth's lower atmosphere (also known as the troposphere, the layer of the atmosphere nearest the earth's surface), ground level ozone is considered bad. Ground level ozone pollution causes human health problems, damages crops and other vegetation, and is a key ingredient of urban smog. Ground level ozone is created by photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs) or hydrocarbons in the presence of sunlight. These reactions usually occur during the hot summer months as ultraviolet radiation from the sun initiates a sequence of photolytical reactions. Ground level ozone can also be transported hundreds of miles under favorable meteorological conditions. Ozone levels are often higher in rural areas than in cities due to transport to regions downwind from the actual emissions of ozone forming air pollutants. Shoreline monitors along Lake Michigan often measure high ozone concentrations due to transport from upwind states.

Ground level ozone is unhealthy to breathe. It can narrow a person's airways, forcing his or her lungs to work harder to provide oxygen to the body. Individuals most susceptible to the effects of ozone exposure include individuals with a pre-existing or chronic respiratory disease, children, and adults who actively exercise or work outdoors. Human exposure to elevated concentrations of ozone can include the following effects:

  • eye irritation
  • difficulty in breathing / shortness of breath
  • aggravated / prolonged coughing and chest pain
  • increased aggravation of asthma
  • increased susceptibility to respiratory infection resulting in increased hospital admissions and emergency room visits
  • Repeated exposures could result in chronic inflammation and irreversible structural changes in the lungs, which can lead to premature aging of the lungs and illness such as bronchitis and emphysema.
  • Growing evidence suggests association with premature death.

Ozone also impacts vegetation and materials. Vegetation and forest ecosystem changes that occur include:

  • agricultural crop and forest yield reductions
  • leaf injury
  • diminished resistance to pests and disease
  • reduced tree seedling survival
  • decreased numbers in species sensitive to ozone

The ozone National Ambient Air Quality Standard was revised by the USEPA on October 1, 2015, to 0.070 ppm and became effective on December 28, 2015. To attain this 2015 standard, the three-year average of the 4th highest daily maximum 8-hour average concentration within an area must not exceed 0.070 ppm.

Attainment designations will be made by the USEPA by October 1, 2017, for the 2015 standard.


DEQ Documents and Resources


USEPA Links and Other Resources