Clean Air Education

What is Ozone?

Ozone is a gas formed when three atoms of oxygen combine. Ozone can occur in the upper atmosphere and near ground level. Depending on where it occurs, ozone can be "good" or "bad".

"Good" ozone is found in the upper atmosphere where it is formed when the more common two atom form of oxygen (O2) reacts with the ultraviolet (UV) radiation from the sun to form three atom oxygen, ozone (O3). This upper atmosphere ozone is beneficial as it forms a protective layer to shield the Earth from dangerous UV rays from the sun.

"Bad" ozone is found near ground level and is considered a "secondary" pollutant- meaning it is not directly emitted, but is formed by a chemical reaction of "formative" emissions. Nitrogen oxides (NOx) and volatile organic compounds (VOC) are the "formative" emissions of ozone. These emissions react in the presence of heat and sunlight to form the detrimental ground level ozone. Ground level ozone is a component of smog and is regulated by the Environmental Protection Agency (EPA). The 2008 standard for 8 hour ozone is set at 75 parts per billion (ppb). Find out more in EPA standards and sources of NOx and VOC.


Sources of NOx and VOC 

NOx are byproducts of combustion, particularly of fossil fuels. Common sources are:

  • automobiles and trucks
  • construction equipment
  • electric utility generation
  • industrial facilities
  • gas powered lawn equipment

VOCs are organic chemicals, containing carbon and hydrogen, which vaporize easily. Common sources are gasoline vapors and solvents including emissions from:

  • gas stations
  • petroleum storage tanks
  • oil refineries
  • biogenics (natural emissions from trees and plants including oaks, pines, sweet gum, and poplars)

Reduction of these emissions reduces the formation of ozone. See the What Can I Do sidebar for more information.

EPA Standards 

The Clean Air Act requires EPA to set National Ambient Air Quality Standards (NAAQS) for pollutants deemed harmful to public health or the environment. These are classified into two groups: primary standards which protect public health including sensitive populations of asthmatics, children, and the elderly and secondary standards that protect public welfare aspects including reduced visibility and damage to animals, crops, vegetation, and buildings. The NAAQS address six principal pollutants.

Pollutant Standard Groups
Carbon Monoxide (CO) Primary
Lead (Pb) Primary and Secondary
Nitrogen Oxides (NOx) Primary and Secondary
Ozone (O3) Primary and Secondary
Particulate Matter (PM) Primary and Secondary
Sulfur Dioxide (SO2) Primary and Secondary

The pollutant of concern for our area is Ozone. The 1997 NAAQS set the standard for ozone at 85 parts per billion (ppb). In 2008, a new standard was developed that strengthened the standard to 75 ppb. EPA makes determinations if areas are meeting the standard, in which case they are designated in "attainment", or not meeting the standard, in which case they are designated "non-attainment". These determinations are based on information from air quality monitoring data, recommendations by states and tribes, and other technical information. If an area is designated "non-attainment", the state and local government is required to take several steps that include stricter controls on industrial facilities, additional planning requirements for transportation related sources, implementation of "transportation conformity" which requires local transportation and air quality officials to ensure that emissions from transportation projects like road construction do not interfere with an area's ability to reach clean air goals, and new source review requirements that require a permitting program for industrial facilities. These steps result in economic consequences and may restrict development in the area designated "non-attainment".

What Can I Do? 

  • Carpool or vanpool to work
  • Minimize vehicle trips by telecommuting, conference calling, or video conferencing
  • Combine errands using trip chaining
  • Bike or walk instead of driving
  • Observe the speed limit
  • Eat lunch at your office
  • Avoid idling your vehicle
  • Wait to refuel your vehicle after sunset
  • Maintain your tire pressure
  • Maintain your vehicle
  • Choose a clean vehicle option if purchasing a new vehicle (electric, hybrid, natural gas, propane, biofuels, and SmartWay)
  • Pursue energy efficient home improvements
  • Switch to compact fluorescent lights
  • Sign up for ozone alert notifications through TCEQ or Air North Texas
  • Join the Air North Texas campaign for free and commit to doing something for clean air
  • Encourage others to do the same
  • Shop local