Unhealthy air quality caused by winter stagnation
An Air Quality Alert was issued Monday for a large portion of Minnesota, for a relatively uncommon reason.
“What we’re experiencing is what we call winter stagnation, which is basically just an air mass that doesn’t have a lot of wind with it, not just at the surface, but up in the atmosphere as well,” explained Minnesota Pollution Agency Research Meteorologist Matthew Taraldsen. “Also the temperature structure of the atmosphere was colder at the surface, warm air above it, and it kind of acts like a lid to kind of trap everything in it. Without the wind, pollution can’t disperse. So it just kind of stacks up.”
The heavy, wet snow that makes up much of the Minnesotan snowpack contributed to the alert lasting for two days.
“All that heavy snow that we’ve got in the past couple of weeks has basically primed the boundary layer,” said Taraldsen. “It’s a low level of the atmosphere full of moisture and that helps to kind of trap those particulates and form particulate matter and then push it down to the surface, so that’s probably the reason why this particular event has been so intense.”
While most of the area under an Air Quality Alert had an Orange Air Quality Index (AQI), these factors led to the Twin Cities having a Red Air Quality Index (AQI) for a portion of the day.
“It is very unusual to have the reds like we had earlier today in the Twin Cities,” said Taraldsen. “We had red AQI from the wildfire smoke a couple of years ago, but this time around it’s just stagnation causing red air quality and mainly in the Twin Cities metro and then in northwest Minnesota as well.”
The Air Quality Index has six categories. Green is for good, clean air, and yellow is for moderate. Orange means that the air is unhealthy for sensitive groups, such as those with asthma. Red is unhealthy for everyone, purple is very unhealthy, and a maroon AQI would mean hazardous air.
“At that orange level, we generally tell people to just avoid strenuous activities outdoors. So in the winter it’s not so much recreation, but shoveling things like that can be really detrimental when the air quality index is orange or higher,” explained Taraldsen. “So those are the really the takeaways we tell people, especially if you’re sensitive to just not push yourself too much outdoors. And if you do, be cognizant of what your body is telling you. If you notice symptoms, slow down, go back inside.”
Symptoms include shortness of breath, sore throat, burning eyes, and developing a cough.
“Those types of things are indications that your body’s working harder to get oxygen, and that’s what air quality does. It degrades the body’s ability to take in oxygen,” said Taraldsen.
The alert expired at 6 pm Wednesday for most of the affected area and was extended until midnight for the Twin Cities and surrounding areas.
“There’s a cold front coming through and that cold front looks to mix up things well enough that we won’t have any issues,” said Taraldsen. “We’re not really expecting things to get worse from here on out, but it’s going to take that front and then a couple of hours following the front for the pollution to really get scoured out.”
Winter stagnation causes an Air Quality Alert once every year or two in minnesota, but that does not mean that we are in the clear.
“The conditions that led to this might occur again this winter, as long as that snowpack is here and temperatures get around that freezing mark with the stump back can release the moisture into the air,” Taraldsen explained. “This could, in theory, happen again if we have the right weather setup. And so it’s something we’re going to be very vigilant and watch for the rest of the season. This year in particular is going to be tricky because we’re going to have that snowpack probably until spring.”
Current air quality conditions can be found here.