Arizona Air Quality Information

Monsoon 2019: Air Quality Recap


Today officially marks the last day of the monsoon season, which runs from June 15 to September 30. For Phoenix, at least Sky Harbor, it was the 5th driest monsoon on record (going back to 1896), finishing with a rainfall total of 0.66". Other local areas around the Valley likely saw more rainfall, but it was overall a rather dry and inactive monsoon for the Valley. This can partially be attributed to the late start of the monsoon this year. However, the Valley was not without some spectacular thunderstorm sights, like the one pictured here from August 28.

Back on August 2, we mentioned that the potential for a strong dust storm during the rest of the monsoon season was small, thanks to widespread rain over the southern deserts in late July. This prediction held up, as PM10 (dust) did not exceed the federal health standard in August or September within the PM10 Maricopa Nonattainment Area (NAA). In fact, PM10 only exceeded the standard once in the NAA this monsoon season--July 11--and only at one monitor (Buckeye also saw PM10 exceed the standard on July 22 because of a dust storm, but it lies just outside the NAA). So, even though the Valley experienced an overall dry monsoon, timely rain helped to reduce the risk for strong dust storms. For comparison, the 2018 monsoon season saw 12 PM10 exceedances; 2017 saw 3.

In regards to ozone, ozone exceeded the federal health standard in Maricopa County on 32 days during the monsoon season. This was 5 fewer exceedance days than last year (37) and 4 more than 2017 (28). Also, the longest stretch of consecutive days when ozone exceeded the standard was 4, which happened twice: July 23-26 and July 30-August 2. This was half of last year's longest stretch of 8 days: August 6-13, 2018.

Keep in mind that all monsoon seasons are different, so we'll just have to wait and see what next year's will have in store for us.