Arizona Air Quality Information

First Moderate Ozone Day of 2023

Yesterday was the first day in 2023 ozone reached the Moderate AQI (Air Quality Index) for Phoenix and Yuma. Tucson saw its first moderate day back on the 27th of February, which is earlier than the average of March 5th. The average first Moderate AQI day in Phoenix is February 19th, with Yuma being March 15th. These three sites are the main ones we focus on regarding ozone, and with each site now having its first Moderate AQI day of the year this raises a question. Now with levels trending towards Moderates across the state, is the ozone season beginning in Arizona?

During the colder months, our main focus is on PM-10 (dust) and PM-2.5 (smoke), due to increased residential fireplace usage and stronger morning inversions. By spring, days become longer with more sunlight, allowing ozone levels to rise as we transition into the warmer months. More sunlight means more hours of the day ozone precursors, such as nitrogen oxides (NOX) and volatile organic compounds (VOCs), can undergo chemical reactions to create surface ozone.

The "ozone season" generally lasts between April and September, encapsulating most of the spring and summer seasons. Between these months we are looking more at the potential for ozone exceeding the federal health standard, not just ozone reaching the Moderate AQI.

Fortunately, we do not expect ozone to exceed in the coming weeks. It may take more time for that to become an area of concern for our air quality forecasts, with Phoenix's average first exceedance occurring on April 20th, and Tucson a month later on May 20th. But with ozone reaching the Moderate category for the first time this year in multiple cities across the state, it does bring ozone back into the picture after a long period of idle activity.

Stay up to date with our daily air quality forecasts to remain informed on our continual monitoring and assessment of rising ozone levels across the state!

Click here to see the latest "Air Quality Hourly Forecast | Phoenix"