Wildfire smoke moving into Colorado from Canada and high ozone levels continue to choke the state Wednesday, prompting alerts for hazardous air quality set to last through Thursday.
As of 2:30 p.m. Wednesday, Denver and most of the surrounding area had air quality index ratings between 100 and 150, according to live tracking data from IQAir.
“When AQI values are above 100, air quality is considered to be unhealthy, at first for members of populations at greatest risk of a health effect, then for the entire population as AQI values get higher (greater than 150),” according to the U.S. Environmental Protection Agency.
Multiple air quality stations in Denver, Arvada and Pueblo reported “unhealthy” AQIs above 150 Wednesday morning.
Conditions worsened in the afternoon — especially in the northern metro area — according to IQAir. As of 2:45 p.m., Arvada hit a “very unhealthy” AQI of 277 and two locations in Louisville reported “hazardous” AQI levels in the mid-500s.
“Avoid all outdoor physical activity,” federal environment officials warned Louisville residents in a Wednesday afternoon alert.
Louisville officially went off the charts for the Environmental Protection Agency at 2 p.m. Wednesday. The EPA’s scale ranges from zero — perfect air quality — to 500+ — extremely hazardous.
At more than 500 PM2.5, the air quality index in Louisville was nearly 16 times higher than the level of particulate matter considered safe by the Environmental Protection Agency, according to the agency’s fire and smoke map.
State officials also reported unhealthy levels of ozone in the Denver area Wednesday morning.
Air monitors across northern Colorado and the Front Range showed high concentrations of particulate matter, which can be smoke, soot, ash or liquid particles that people can inhale.
Denver air monitors Wednesday recorded rates of particulate matter nearly seven times higher than the level considered safe by the EPA, according to the agency’s fire and smoke map.
State health and air quality officials issued a “multiple pollutants” action day alert Tuesday that was scheduled to last through 4 p.m. Wednesday.
Warm and stagnant weather combined with increasing amounts of out-of-state wildfire smoke will result in ozone and fine particulate matter concentrations reaching unhealthy levels for air quality, Colorado Department of Public Health and Environment officials said in the action day alert.
The air quality advisory was initially issued for Douglas, Jefferson, Arapahoe, Denver, Adams, Broomfield, Boulder, Larimer and Weld counties through 4 p.m. Wednesday, but poor air quality across Colorado quickly expanded the alert.
At 9 a.m., the “multiple pollutants” action day alert expanded to include Teller, El Paso, Fremont, Pueblo, Kiowa, Bent, Otero, Sedgwick, Logan, Phillips, Morgan, Yuma, Washington, Elbert, Lincoln, Kit Carson, Cheyenne, Custer, Huerfano, Las Animas, Baca, Gilpin, Clear Creek and Park counties.
“Heavy smoke will result in elevated concentrations of both ozone and particle pollution through at least Thursday morning,” state officials said.
State health officials also extended the length of the alert, moving the end of the “multiple pollutants” action day to 4 p.m. Thursday.
Where possible, people should limit driving gas and diesel-powered vehicles until the action day expires, the alert stated.
“People with heart or lung disease, older adults and children should avoid prolonged or heavy exertion and limit time outdoors,” state officials said in the alert. “Everyone else should reduce prolonged or heavy exertion and, while outside, take more breaks.”
State officials said people should stay inside if smoke becomes thick in their neighborhood and should consider temporarily relocating if smoke is present indoors or making residents ill.
If visibility is less than 5 miles due to smoke in the area, the air quality has reached unhealthy levels, state officials said.
Thick smoke is expected to hang around Colorado through Thursday, according to the National Weather Service. Forecasters said better conditions are expected by Friday.
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