Ozone season typically runs from March to November in Texas. Each day during ozone season, the TCEQ informs the public when forecasted conditions can lead to Ozone Action Days (OAD). These are days when ozone levels are expected to be elevated and can impact the public’s health through the quality of the air.
Ozone, sometimes referred to as smog, is a gas formed in the atmosphere when three atoms of oxygen combine. The chemical structure of ozone is the same wherever it is found; however, there are two categories of ozone: Stratospheric and ground-level.
- Stratospheric ozone is found naturally in the Earth’s upper atmosphere — six to 30 miles above the Earth’s surface — where it forms a protective layer that shields us from the sun’s harmful ultraviolet rays.
- Ground-level ozone, also called tropospheric ozone, is found at ground level. It is not emitted directly into the air but is created by chemical reactions between oxides of nitrogen (NO and volatile organic compounds (VOCs) in the presence of sunlight. Emissions from industrial facilities, electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are some of the major sources of NO and VOCs. In addition, biogenic sources (living organisms or biological processes) release VOCs that can contribute to ground-level ozone.
Ground-level ozone is important because it is a respiratory toxic agent that can cause acute respiratory health effects when people breathe high concentrations of it over several hours. These effects can include decreased lung function and pain with deep breaths, as well as aggravated asthma symptoms
TCEQ meteorologists make daily OAD forecasts during the OAD forecast season for each of the following nine metropolitan areas in Texas: Austin, Beaumont-Port Arthur, Corpus Christi, Dallas-Fort Worth, El Paso, Houston, San Antonio, Tyler-Longview, and Victoria.
The OAD forecast seasons are based on when each region is likely to experience elevated ozone concentrations. Each forecast predicts whether ozone levels for the following day in an area are expected to (but does not guarantee that they will) reach or exceed the EPA’s Air Quality Index Level Orange — an eight-hour average of 71 parts per billion or a one-hour average of 125 ppb.
TCEQ meteorologists use a set of criteria from historic meteorological data, ozone measurements, and ozone prediction models to make these predictions. When they forecast an OAD, TCEQ meteorologists contact the National Weather Service, which then broadcasts the information across its “weather wire.” TCEQ also contacts officials in affected areas so that local community clean air coalitions can notify their media, government, businesses, and industry. OADs are issued, in most cases, by 2 p.m. local time and are valid for the next day.
Tips to Decrease Ozone
- Limit driving and idling. Instead, carpool, combine errands, use public transportation, bike, or walk.
- Refuel your vehicle in the late afternoon or evening and don’t top off the tank.
- Keep your vehicle maintained, including proper tire pressure.
- Maintain your yard equipment, including changing the oil and replacing air filters regularly. Also consider using tools without motors. Hand tools such as shears, edgers, and push reel mowers are lightweight, quiet, and easy to use, and do not generate emissions.
- Don’t burn yard waste.
- Use paint and cleaning products with lower zero volatile organic compounds.
Sign up for e-mail and text alerts about TCEQ’s Air Quality Forecast and other topics on the TCEQ newsletter page.
You can also sign up to receive e-mail alerts through the EPA EnviroFlash website.
This article was adapted from a post on the Take Care of Texas blog.