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Harris County Ozone

road sign March through October is ozone season in the greater Houston area. Sign up for email ozone alerts here.


The EPA has designated Harris County as being in moderate nonattainment of its 8-hour ozone standard. Harris County participates with other state and local agencies in maintaining a monitoring network to provide the public with current ozone data and advisories.

Ozone (O3) is a compound containing three oxygen atoms. Molecules of normal oxygen (O2) are composed of two oxygen atoms. Ozone can be found in the upper atmosphere and at ground level. It occurs naturally in the upper atmosphere where it blocks harmful UV radiation. It forms at ground level when pollutants react to form photochemical smog. Ozone is highly reactive and at high concentrations it may corrode metals, degrade plastics, and cause respiratory irritation.

downtown Ozone is a major component of photochemical smog

Ozone forms at ground level when nitrogen oxides and volatile organic compounds combine in the presence of sunlight. Nitrogen oxides are found in car exhaust and industrial emissions. Volatile organic compounds enter the atmosphere from industrial emissions, paints and solvents, evaporated gasoline, and natural sources. The ideal conditions for ozone formation are hot, clear days with calm winds.

ozone formation

Ground level ozone can cause inflammation of the lungs and repeated exposure to high levels may cause scaring of lung tissue and diminished lung capacity. Some studies have also linked ozone exposure to increased incidence of heart attack and respiratory infection. Sensitive individuals such as people with respiratory conditions, parents of young children, and the elderly should pay close attention to ozone warnings and avoid outdoor activity when ozone levels are high. Strenuous outdoor exercise should also be avoided when ozone levels are high.

You can assist in reducing ozone levels in Harris County. Maintain your vehicle to reduce emissions. Purchase gasoline and mow your lawn in the evening so that vapors dissipate when solar radiation is low. Use public transportation where available. Turn off unnecessary lights and appliances to reduce emissions from power plants. It will take the cooperation of the public, industry, and regulatory agencies to restore our air quality in Harris County. Please do your part.

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