Skip to Main Content


What is Ozone?

Ozone is a colorless gas that can be found in the air we breathe. Each molecule of ozone is composed of three atoms of oxygen, one more than the oxygen molecule which we need to breathe to sustain life. The additional oxygen atom makes ozone extremely reactive. Ozone exists naturally in the earth's upper atmosphere, the stratosphere, where it shields the earth from the sun's ultraviolet rays. However, ozone found close to the surface of the earth, called ground-level ozone, is harmful air pollution.

Ozone is formed by a chemical reaction between volatile organic compounds (VOCs) and oxides of nitrogen in the presence of sunlight. Sources of VOCs and oxides of nitrogen include:

  1. automobiles, trucks and buses
  2. large industry and combustion sources such as utilities
  3. small industry such as gasoline dispensing facilities and print shops
  4. consumer products such as paints and cleaners
  5. off-road engines such as aircraft, locomotives, construction equipment and lawn and garden equipment.

Ozone concentrations can reach unhealthy levels when the weather is hot and sunny with relatively light winds.

Health Effects

Even at relatively low levels, ozone may cause inflammation and irritation of the respiratory tract, particularly during physical activity. The resulting symptoms can include coughing, throat irritation, and breathing difficulty. Inhaling ozone can affect lung function and worsen asthma attacks. Ozone can increase susceptibility of the lungs to infections, allergens, and other air pollutants. Medical studies have shown that ozone damages lung tissue and that after exposure has ended complete recovery may take several days.

Groups that are sensitive to ozone include children who are active outdoors, outdoor workers, people with respiratory diseases, such as asthma. Sensitive people who experience effects at lower ozone concentrations are likely to experience more serious effects at higher concentrations.

Ozone Standards

On March 12, 2008, EPA strengthened its national ambient air quality standards (NAAQS) for ground-level ozone, the primary component of smog. The standard is 0.075 parts per million (ppm), which is determined by the annual fourth-highest daily maximum 8-hr concentration, averaged over 3 years. The previous standard, set in 1997, was 0.08 ppm.

Ozone Data

All files are in excel format.

The Western North Carolina Regional Air Quality Agency maintains one ozone monitoring station located at Bent Creek. Daily ozone readings from this site have been maintained since 1989. The data on this website is raw data that has not been validated. For official data, please visit

Table: Ozone Monitoring Site Information
Ozone Monitoring Site Information
Site Name: Bent Creek
AIRS ID Number: 37-021-0030
County: Buncombe
Elevation in Feet 2215
Latitude: 35.505248
Longitude: -82.59718
Years of Operation: 1989 - Present