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Pollutants

Ozone (03) - 8 Hour Standard

National Ambient Air Quality Standard – 0.075 parts per million (ppm) – 3-year average of the 4th highest 8-hr concentration.

Ozone is a gas composed of three atoms of oxygen. Ozone occurs both in the Earth's upper atmosphere and at ground level.

Ozone can be good or bad, depending on where it is found:

  • Good Ozone
    Ozone occurs naturally in the Earth's upper atmosphere-6 to 30 miles above the Earth's surface-where it forms a protective layer that shields us from the sun's harmful ultraviolet rays. This beneficial ozone is gradually being destroyed by manmade chemicals. An area where the protective "ozone layer" has been significantly depleted-for example, over the North or South pole-is sometimes called "the ozone hole."
  • Bad Ozone
    In the Earth's lower atmosphere, near ground level, ozone is formed when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources react chemically in the presence of sunlight. Ozone at ground level is a harmful air pollutant.

Air Quality Index (AQI): Ozone

Index Values

Levels of Health Concern

Cautionary Statements

0-50

Good

None

51-100*

Moderate

Unusually sensitive people should consider reducing prolonged or heavy exertion outdoors.

101-150

Unhealthy for Sensitive Groups

Active children and adults, and people with lung disease, such as asthma, should reduce prolonged or heavy exertion outdoors.

151-200

Unhealthy

Active children and adults, and people with lung disease, such as asthma, should avoid prolonged or heavy exertion outdoors. Everyone else, especially children, should reduce prolonged or heavy exertion outdoors.

201-300

Very Unhealthy

Active children and adults, and people with lung disease, such as asthma, should avoid all outdoor exertion. Everyone else, especially children, should avoid prolonged or heavy exertion outdoors.

301-500

Hazardous

Everyone should avoid all physical activity outdoors.