HOUSTON (KIAH) – The number of stagnant-air days has been on the rise in recent decades, which is no surprise as summers have been getting hotter in Houston.

Higher temps leads to more stagnant air days in Houston (Climate Central)

An air quality alert is in effect for Houston, Austin, San Antonio and Dallas on Wednesday as sunshine, warm air and relatively light winds allow ozone levels to reach “unhealthy for some” levels, also known as an “ozone action day”.

Air quality alerts Wednesday
Air quality alert Wednesday, similar through Friday

The Texas Commission on Environmental Quality (TCEQ) expects similar stagnant air conditions through Friday.

It’s not just Houston experiencing more stagnant-air days, but also much of Texas and the U.S. The orange and red areas in the image below show where stagnant-air days have increased in the last 50 years. The biggest increase has occurred in Texas and California.

Change in stagnant-air days since 1973 (Climate Central)