Arizona Air Quality Information

First Ozone Exceedance for Phoenix in 237 Days


On Friday, May 3, ozone exceeded the federal health standard for the first time this year in Phoenix. Six ozone monitors in east and northeast parts of the Valley saw exceeding ozone levels that day. Weather-wise, a light wind pattern over the region enabled ozone levels to accumulate near the ground.

A unique fact about the timing of this exceedance was that it occurred just shy of the record for a given year's latest first ozone exceedance. This record currently stands at May 4, set back in 2010. Thus, this now makes May 3, 2019 the second latest first ozone exceedance of a given year, since 1980.

Moreover, the last time ozone exceeded the federal health standard was on September 7, 2018. That means 237 days passed without ozone exceeding the health standard. This was the fourth longest stretch without an ozone exceedance, since 1980.