Colorado’s air quality health advisory in the northern Front Range, including Denver and Boulder, has been in effect since Monday afternoon, sparking questions about why the area experienced such high levels of pollution.
Under the advisory, people with heart or lung disease, older adults and children are advised to limit prolonged or heavy exertion.
On Thursday, the Colorado Department of Public Health declared an Action Day for Particulates and Visibility in the Denver metro area, in which the area enforces certain pollution prevention measures including residential burning restrictions. Visibility in the area is also impacted: The Denver Post described a “brown cloud” hanging over downtown Denver.
Scott Landes, supervisor of the meteorology and prescribed fire unit at the Colorado Air Pollution Control Division, says he expects the advisory to be lifted by Saturday.[
“It’s going to be a tough call (for this evening) we’re waiting to see what happens this afternoon,” he says, adding that a storm moving in overnight will clear the health threat by the morning.
Landes says this week’s high pollution levels stem from a combination of factors, with the major meteorological factor being a temperature inversion, cold air near the surface of the Earth and warmer air overhead. He says the warmer air acts like a lid, trapping emission sources and other pollutants below.
Though this week’s advisories have gained a great deal of attention, high pollution levels from temperature inversions aren’t a new phenomenon for Denver. Landes says these temperature inversions occur in the winter and usually last one or two days. For example, the metro area experienced an air quality health advisory in January (though the pollution levels were far lower then)..
“The things that make this situation different or unusual is how late in the winter it’s occurring, and the reason for that is we’ve had surface temperatures anywhere from 20 to 30 degrees before normal for this time of year earlier this week,” Landes says. He adds that this inversion is also lasting longer than usual.
The northern Front Range unique topography, which Landes says tends to be insulated from stronger winds and is more prone to temperature inversions, along with the city’s large population, means the area is more likely to experience these periods of poor air quality than other regions.
In 2017, Denver established a Mobility Action Plan, with a goal of reducing single-occupancy vehicle commutes from 73 percent to 50 percent.
But some residents say the city isn’t doing enough to ensure a safe environment with clean air.
Many Denver residents have taken to Twitter to express their frustration with the city’s air quality conditions: