The surprising data on air quality in the West

An inversion begins to fill the Salt Lake Valley on Monday, Nov. 29, 2021. With wildfire smoke filling the summer skies in recent years on top of the perennial winter inversions trap pollution in populated valleys, it would seem air quality has worsened in the past decade. Or has it? | Scott G Winterton, Deseret News

The average number of total unhealthy days across Arizona, Colorado, Idaho, New Mexico, Nevada, Utah and Wyoming in 2020 was less than it was in 2010.

With wildfire smoke filling the summer skies in recent years on top of the perennial winter inversions trap pollution in populated valleys, it would seem air quality has worsened in the past decade.

Or has it?

The federal Environmental Protection Agency said concentrations of air pollutants have dropped “significantly” since 1990. And over the past decade in the Intermountain West, days rated as variants of “unhealthy” in the EPA’s Air Quality Index dropped to new lows in 2019, a Deseret News analysis found.

Adding up days designated as “unhealthy for sensitive groups,” “unhealthy” and “very unhealthy,” the average number of total unhealthy days across Arizona, Colorado, Idaho, New Mexico, Nevada, Utah and Wyoming in 2020 was less than it was in 2010.

“The Air Quality Index tells you how clean or polluted your outdoor air is, along with associated health effects that may be of concern,” EPA spokesperson Melissa Sullivan said in an email. “Millions of people live in areas where air pollution can cause serious health problems.”

Overall, Arizona had the worst air quality of any state in the Intermountain West with the average of unhealthy days per year reaching nearly 20, double that of second place Utah.

And that ranking comes without data from Maricopa County, Arizona’s most populated area, which was excluded from the past decade’s data because the EPA said the results “are not reliable” due to “anomalous, elevated ozone concentrations from one monitor.”

“We are working with the reporting agency to resolve the issue,” Sullivan said.

Although air quality data goes through a quality assurance procedure, it isn’t always reliable because of delays in reporting, state data gathering and reporting methods, faulty monitors or other anomalies.

“Like all tools, the AQI is only as good as the data used to drive it,” Sullivan said. “It is the best tool available to communicate air quality levels to the general public and has been used for over 20 years. Because of its reliability it has been adopted and imitated worldwide.”

Regarding methods varying by state, some do not consistently report data for all counties and might not track all pollutants.

“States choose to site monitors in areas with higher concentrations and/or higher population since the minimum monitoring requirements are based on population size,” Sullivan said. “Therefore, not all counties have monitors from one year to the next (and those that do have monitors do not necessarily measure every pollutant).”

There’s a noticeable dip in average unhealthy days across the Intermountain West in 2019, something the EPA attributes to fewer wildfires.

“The air quality, specifically particulate matter pollution, in most (if not all) of those states was impacted by high wildfire activity in 2017 and 2018, and again in 2020,” Sullivan said.

And in 2013, Utah had an uptick in average total unhealthy days, something that the EPA can’t explain.

“Unfortunately, we do not have information regarding a 2013 uptick in Utah,” Sullivan said.

As far as the good days over the past decade: In 2010, Clear Creek County, Colorado, only had four “good” days reported. But in 2012, Taos County, New Mexico, had all 365 days classified as “good.”

In 2011, Pima County, Arizona, had 22 “very unhealthy” days — the most out of any county in the Intermountain West during the past decade.

Last year, three counties in Idaho — Kootenai, Nez Perce and Shoshone — had the most “very unhealthy” days with four days each.

According to the EPA, “very few locations (about 0.3% of counties) have any days in the very unhealthy or hazardous categories.”

Wyoming consistently has the least “unhealthy” days around the region with little average variance over the decade.

Check the EPA data on how the air quality in your county has been changing:

K. Sophie Will is a Deseret News contributor. @ksophiewill