The National Weather Service has issued air quality alerts for millions in Texas, urging reduced vehicle use on Monday. The alerts cover the Dallas-Fort Worth area and regions like Houston, Galveston, and Brazoria. The notice warns of atmospheric conditions likely to elevate ozone levels, a harmful pollutant.
Residents are encouraged to minimize ozone pollution by carpooling, walking, biking, bringing lunch from home, avoiding drive-throughs, conserving energy, and maintaining vehicles well. These recommendations coincide with Ozone Action Days announced for the affected areas.
Understanding Ozone Action Days
Ozone Action Days align with periods when regions expect high ozone levels. Forecasters use the EPA’s AQI Level Orange threshold to determine these days. This level is defined as an eight-hour ozone average of 71 parts per billion or a one-hour average of 125 ppb.
The Texas Commission on Environmental Quality (TCEQ) uses historical weather data, ozone monitoring, and models for this assessment. Upon issuing an alert, TCEQ coordinates with the National Weather Service for dissemination.
What is Ozone?
Ozone, a secondary pollutant, forms from chemical reactions in the presence of sunlight and higher temperatures. This is more prevalent in warmer months. Stagnant air prevents pollutant dispersion, leading to unhealthy ozone levels.
According to AccuWeather meteorologist Brandon Buckingham, ozone or smog consists of gases in the atmosphere. Ozone falls into two categories: stratospheric and ground-level. While the ozone structure remains the same, stratospheric ozone offers a protective shield from harmful UV rays. Ground-level ozone results from chemical reactions with nitrogen oxides and volatile organic compounds.
Health Risks of Ground-Level Ozone
The EPA highlights that individuals with asthma, children, older adults, and outdoor workers are most vulnerable to ozone exposure. Effects range from coughing and sore throats to difficulty breathing and airway inflammation.
Ground-level ozone can also exacerbate lung conditions like asthma, emphysema, and bronchitis, increasing the frequency of attacks.
Measuring Air Quality with the AQI
The EPA uses the Air Quality Index (AQI) to gauge air quality in the U.S. The scale ranges from 0 to above 301, classifying air quality from good to hazardous levels:
- Green—Good (0 to 50): Air quality poses little or no risk.
- Yellow—Moderate (51 to 100): Acceptable air quality with a minor risk for sensitive people.
- Orange—Unhealthy for Sensitive Groups (101 to 150): Sensitive groups could experience health effects, but the general public sees less risk.
- Red—Unhealthy (151 to 200): Some in the general public may face health effects; sensitive groups could face more severe impacts.
- Purple—Very Unhealthy (201 to 300): An increased health effect risk for everyone.
- Maroon—Hazardous (301 and higher): Health warnings; more likely to affect everyone.
The article update was on 5/25/2026 at 5:30 a.m. ET incorporating new information.