The Colorado Department of Public Health and Environment officials say apps like the one from IQAir, a Swiss air filter manufacturer, give only momentary readings that can be a misleading basis for rankings. They also use equipment that isn't uniformly calibrated and data that isn't always verified.
"Air quality in a particular area can vary considerably over time and, because of this, it's not surprising that the air quality in Denver may be worse than in heavily polluted cities temporarily at any given point in time," Colorado Air Pollution Control Division director Garry Kaufman said. "It's problematic to draw comparisons between air quality in Denver and these other places without looking at pollution levels over much longer periods."
If you're concerned about air quality, state officials recommend checking CDPHE-vetted information from 16 measuring stations via colorado.gov/airquality or tracking readings on the U.S. Environmental Protection Agency's site — airnow.gov — which includes data collected at embassies worldwide and allows international comparisons.
Nobody's disputing that the unhealthy air quality in Colorado Front Range cities has deteriorated over the past two years. This summer, health officials have issued a record 57 air quality advisories, one every day since July 4th except for Aug. 15 and Aug. 19.
For more than a decade, Colorado air has flunked federal health standards due to elevated ground-level ozone pollution. State residents also face intensifying surges of particulates from western wildfires that have obscured mountain views — with more anticipated depending on wind as wildfires in northern California grow.
But air quality in Denver simply isn't as bad as in Asia, Colorado officials said, pointing to state and federal data.
Even a look at IQAir's data, collected over an entire year instead of the momentary rankings, confirms this. In 2020, Denver air did not rank in the top 15 worst cities for air pollution in North America, let alone the world, according to the company's latest annual "world air quality" report.
Among 4,744 cities worldwide, Denver ranked 3,279th. The top cities were: New Delhi, India; Dhaka, Bangladesh; Ulaanbaatar, Mongolia; Kabul, Afghanistan; and Doha, Qatar.
IQAir is run by a Switzerland-based air filter manufacturer that also operates data sites drawing from 80,000 measuring stations (400 in Colorado). Many of them are private, but EPA and CDPHE stations are included, company spokeswoman Tiffany Allegretti said.
Colorado officials have "a valid point," Allegretti said. The rankings are "fixed in that moment" and measuring equipment and methods aren't all the same.
"We're in the business of letting people know about their air quality. The more you know, the better decisions you can make," she said. "We want people to check their air like they check the weather."
IQAir officials say city rankings aren't meant to "brand" a city with bad air and, last year, the company began working with the United Nations on data platforms that reach 15 million people.
"Combining air quality data and filtration, we can help people control and improve the environment," IQAir North America chief executive Glory Dolphin Hammes told The Denver Post. "Our mission is to help minimize exposure to air pollution."
Bad air often is measured using the Air Quality Index (AQI), which was developed by the EPA. But Colorado Air Pollution Control Division meteorologist Dan Welsh said the AQI can be problematic because it factors in only the single most elevated pollutant detected in an area, such as the particulates 2.5 microns wide that increase during wildfires.
Yet metro Denver and Colorado Front Range smog contains multiple pollutants at once — typically elevated ozone and particulates. That means AQI readings at times may not fully reflect how bad pollution may be and the health threats, Welsh said.
"There's just lots of nuance and context with any air quality assessment," he said. "So much depends on what monitors you're using. We base our data only on federally approved, tested and vetted monitors."
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