Minneapolis air quality dips as morning commute’s pollution is trapped at ground level

A wintertime inversion trapped fine particles close to the ground, but conditions improved through the day.

The Minnesota Star Tribune
February 21, 2024 at 5:31PM
A smoky haze enveloped Minneapolis seen from the south across I-35W Wednesday, June 14, 2023 Minneapolis, Minn. Smoke from Canadian wildfires blowing into Minnesota is making for a bad air day. The MPCA has issued an air quality alert covering the northern half of the state, the metro area and a portion of southern Minnesota.
A smoky haze enveloped Minneapolis on June 14, 2023. Air quality problems have been frequent in Minnesota of late, though it's not always caused by the same factors. An air quality alert on Wednesday was triggered by traffic pollution lying low to the ground thanks to a weather phenomenon known as inversion. (Glen Stubbe, Star Tribune/The Minnesota Star Tribune)

Parts of the Twin Cities area woke up to unhealthy air quality on Wednesday morning, as a classic wintertime inversion pushed pollution from vehicle tailpipes close to the ground.

Minnesota Pollution Control Agency air quality meteorologist David Brown said that stagnant air across the state and a relatively mild weather pattern allowed the fine particles to linger, when normally wind would have diluted the pollution and whisked it away.

“The emissions that cause this tend to happen most in the morning,” Brown said, as people across the region drove to work.

A monitor in Minneapolis’ Phillips neighborhood reached an air quality index (AQI) of 166 at 8 a.m. Wednesday, and another sensor on NE. 3rd Street in Minneapolis reached 151 at the same time. Both readings are in the red classification of AQI, meaning the air is unhealthy for all people to breathe.

But around 11 a.m., sensors in parts of south and northeast Minneapolis showed improving air in the orange AQI category — meaning it was unhealthy only for sensitive groups, including people with breathing and cardiovascular problems.

Wintertime inversions are not new in Minnesota. One extreme example in January 2023 sparked an air quality alert for much of the state and spread a yellowish haze across the metro area. But smoke drifting south from Canadian wildfires drove much of Minnesota’s declining air quality last year, sparking a record number of bad air alerts from the MPCA.

It’s not yet clear what kind of smoke season 2024 will bring, Brown said, but conditions in Canada are similar to this time last year — warm and dry, raising the risk that fires could spark before green plants emerge, which helped contribute to last year’s rash of blazes.

Forecasters are also watching reports of “zombie fires” that burn in the peat of boreal forests, even under layers of snow. The BBC recently reported that residents of northern Canada are already reporting smoky smells, indicating a record number of overwintering fires.

Brown said he expects Canadian officials to start issuing fire season outlooks in March, and MPCA will release its own smoke forecast later in the spring.

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about the writer

Chloe Johnson

Environmental Reporter

Chloe Johnson covers climate change and environmental health issues for the Star Tribune.

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