Minnesota is experiencing the worst wildfire smoke in at least recent memory and possibly ever.
A dense, unhealthy cloud of smoke began descending south across the state Monday, July 13, from multiple wildfires burning in the Superior National Forest and Boundary Waters Canoe Area Wilderness north of Ely.
The Minnesota Pollution Control Agency has been using monitors across the state to measure air quality for decades. It started keeping records back in 2014.
"You're talking about all of these past wildfire events, smoke events, that we've experienced in Minnesota — in 2021, in 2023, in 2025 — nothing has come close to what we're measuring with this event," said PCA meteorologist Ryan Lueck.
In terms of smoke, air quality is measured by the concentration of fine particles in the air, called PM2.5 — particulate matter that is 2.5 micrometers or less in diameter.
Minnesota's previous record was set last year in Grand Portage at 476.2 milligrams per cubic meter.
As of Thursday morning, July 16, the new record was 797.5, measured in Ely.
Those numbers might seem different than the readings you've seen when checking the air quality where you're at.
The PCA uses two other measurements. One you're probably familiar with: the air quality index or AQI. That's measured on a scale of 0-500 and is a daily average of air quality.
AQI is designed to communicate just how bad the air quality might be, which is why it's broken up into color categories, too. For example, maroon is hazardous air quality over 300 AQI.
There's also the NowCast AQI. Lueck called it a bridge between the hourly concentration measurements and the daily AQI. It takes the measurements from the last few hours and converts them to the AQI scale.
"It's all trying to tell you the same thing," Lueck said. "Once you see numbers that are really high, it's just bad air quality, and sometimes if it's confusing, it's just better to rely on the colors."
The PCA forecasts unhealthy to hazardous air quality for Northern Minnesota through at least midday Monday.
Heavy smoke may linger longer in northeast Minnesota.
When air quality is hazardous, the PCA says to avoid physical activity outdoors. Sensitive groups should stay indoors, keep activity levels low and keep indoor air as clean as possible.
The same general principles apply for unhealthy and very unhealthy air quality.
