High school coaches and administrators across Minnesota have been asked to be aware of air-quality levels as athletes return to practice.

Practices were permitted for the first time Monday and have gone on as scheduled while state health and pollution control agency officials keep a close eye on 700 wildfires burning across Canada.

On Wednesday, the Minnesota Pollution Control Agency said air quality had improved and was below the alert threshold across northern Minnesota and that air quality would continue to improve across the state over the next few days.

Moderate levels of smoke continued to impact northern and central Minnesota on Wednesday, the agency said, but it cancelled an air-quality alert that went into effect for the entire state Monday morning.

The United States’ air-quality index (AQI) is on a scale of 0 to 500; the higher the number the worse the air. An AQI over 300 represents hazardous air quality, but concerns begin at much lower levels; an AQI above 100 is considered unhealthy. On Monday, Bemidji checked in at 179.

On Wednesday, the index was at 132 for northwestern Minnesota and Red River Valley North, and for the Duluth area and north-central Minnesota it was at 117, which is considered unhealthy for sensitive groups, according to airnow.gov.

“We’ve been fortunate this week,” Duluth Denfeld football coach Erik Lofald said. “It was looking like [Wednesday] was really going to push into maybe that high red zone. If you get into the 150s and 160s, that’s when you have to really consider not maybe cancelling but really limiting your practices or moving inside. You get into that 200 area and we’re talking we can’t be outside at all. Yesterday was really the first day when we were like, ‘We may have to adjust here,’ and then it turned out to be a really nice day. It turned out to be windy and cooler.”

The AQI also uses a color scheme to indicate levels of seriousness. Thursday’s forecast showed only green (good) and yellow (moderate) for all of Minnesota as lingering smoke leaves the state; winds on Thursday are expected to push remaining smoke north.

Air quality is expected to move into the green category for the rest of the state by Friday and Saturday.

“They’ve been telling us to keep an eye on the air quality and when it gets to a certain limit, the boys have to stop practicing,“ Brooklyn Center football coach Rodney Pierce-Tyler said. ”We have been splitting up practice, half start inside and half outside. We have a trainer on hand out there that’s keeping an eye on it. When she says to shut it down, we have to shut it down. We’re taking every precaution when it comes to the kids’ safety.”

Hermantown girls soccer coach Nate Hanson on Wednesday said his team had yet to experience issues with air quality.

“We’ve been [practicing] in the morning and it hasn’t affected us,” he said.

Per Minnesota State High School League guidelines, outdoor activity should be moved indoors when the AQI reaches 150 and moved indoors, canceled or postponed when the number reaches 200.

An AQI of 100 or less is considered acceptable for usual athletic activities, according to the league. An AQI above 100 is considered unhealthy, at first for athletes and coaches with respiratory or cardiac conditions and for everyone as the AQI increases.

“People that have lung issues in general are ones that often are more reactive to the worst air quality, but at some point, it’s really not healthy for any of us,” said Dr. Nick Simpson, Hennepin Emergency Medical Services’ chief medical director.

The MSHSL’s recommendations for air-quality levels include:

• Any athlete or team personnel who develops a cough, chest tightness, wheezing or shortness of breath should not exercise outside when the air quality is bad.

• Athletes with asthma should move indoors for an AQI of 100 or above.

• Moving everyone indoors when the AQI is above 150 is recommended.

• When the AQI is greater than 200, all outdoor activities should be moved indoors, postponed or cancelled.

Simpson compared the decision to cancel high school practices because of poor air quality to the decision race organizers face with heat advisories. General threshold guidelines exist, “but typically it’s up to the race director or the medical director of that event to make those calls” or put out guidance for participants to ease up on the effort of their activity. In this case, that’s coaches and athletic directors.

“The big thing for coaches … is just to be vigilant and to have an awareness of what medical issues the participants in these events have,” Simpson said.