Sign In

Houston Ship Channel

Harris County is a designated nonattainment area for the EPA’s 8-hour ozone standard. Harris County and other state and local agencies participate 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.

Ozone Information

Ozone Formation

Ozone forms at ground level when nitrogen oxides (NOx) and volatile organic compounds (VOC) combine in the presence of sunlight. NOx is found in car exhaust and industrial emissions. VOC enters 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.

Stay informed

Daily air quality forecasts, provided by the TCEQ can be found here

A map with current ozone levels in Harris County can be viewed here.

What to do when ozone levels are high

Ground level ozone can cause inflammation of the lungs. 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.

Ozone Level Downtown
You can help

You can assist in reducing ozone levels in Harris County. Maintain your vehicle to reduce emissions. Fill your gas tank and mow your lawn in the evening when ozone formation is low. Use public transportation where available. Conserve electricity 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. Thank you for doing your part.

Air Quality Links  

​Ozone Links 

For suggestions or comments regarding this site please email us at

The information contained in this site was valid at the time of posting. Harris County assumes no liability for damages incurred directly or indirectly as a result of errors, omissions or discrepancies. Moreover, Harris County is not responsible for the content nor endorses any site which has a link from this page. For additional information please review our Privacy Policy and our Accessibility Statement.