Arizona Air Quality Information

Published on: 01/16/2020 at 11:43 AM by M. Graves

2019: Phoenix Air Quality Year in Review


2019 was a relatively good year for air quality in Phoenix. Now, the air quality wasn't perfect, but Phoenix did manage to escape some of the extremes that it saw in recent years (photo to the left: highest ozone day of 2019, with monsoonal storms to the north of Camelback Mountain).

Let's take ozone for example. In 2019, ozone exceeded the federal health standard on 39 days. Since 1980, there have only been ten years that had fewer ozone exceedance days than 2019 (using the current standard of 70 ppb). For comparison, 2018 had 53 ozone exceedance days. The graph to the right shows the total number of exceedance days for each year between 1980 and 2019, with years ordered by total number of exceedance days, from least to most. Click the graph for a closer look.

Another significant story for ozone in 2019 was the delay in the first ozone exceedance day of the year. 2019 came just one day shy of the record for the latest first ozone exceedance (May 4), given the current standard. An active jet stream helped to prevent ozone exceedances in the spring. However, the occurrence of the last ozone exceedance day of the year was relatively normal, falling in early September.

[Read more: First Ozone Exceedance for Phoenix in 237 Days]

The biggest thing to note for PM10 (dust) is how Phoenix escaped the Monsoon season without a major dust storm. This was due to widespread rain in late July. The picture to the left shows dust north of the Estrella Mountains on April 9, one of 2019's three PM10 exceedance days.

[Read more: Phoenix AQ History: Dust Storm Causes Hazardous Air Quality]

Moreover, PM10 levels ended up being low throughout much of January, February, the second half of November, and much of December, helped out by rain. Rain limited the number of Moderate Air Quality Index (AQI) days during each month. For instance, Phoenix only had 4 Moderate AQI days for PM10 in December, which tied for the third lowest monthly total, since 1997.

Last but not least, in regards to PM2.5 (smoke and soot), Phoenix had its longest streak of days without PM2.5 exceeding the health standard, since 2010. This streak lasted 370 days, from December 26, 2018 to December 30, 2019. Active weather occurring over New Year's Eve/Day in 2018/19 and Christmas Eve/Day in 2019 helped to extend this streak.

[Read more: Christmas 2019: Best Air Quality in Phoenix]

The graph to the right shows hourly PM2.5 levels on New Year's Eve--when the aforementioned 370 day streak ended--for various monitors in Phoenix. Notice how PM2.5 levels shot way up toward midnight, due to holiday festivities. PM2.5 also remained almost entirely in the Good AQI category in the summer as Phoenix avoided any major dust storm.