Ask Planet Detroit: Why was Detroit’s air so bad in December?

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A couple of elevated readings in the air quality index looked concerning

Dear Planet Detroit,

The air quality index (AQI) in Detroit was elevated on Dec. 10 and 11, with readings of 155 and 120 AQI. What is the cause?


Curious about what we’re breathing

Dear Curious,

Lots of factors can contribute to air quality, so let’s break those numbers down and try to figure out what it means. 

The Air Quality Index (AQI) rating is monitored by the U.S. Environmental Protection Agency, with support from local agencies, and based on the atmospheric concentration of six pollutants: nitrogen dioxide (NO2), ozone (O3), sulfur dioxide (SO2), particulate matter (PM), carbon monoxide (CO), and lead (Pb). It then assigns a number on a scale of 0-500, which is broken up into six levels of health concern. 

If the AQI is under 150, the atmosphere is generally considered to be harmful only to sensitive groups including the elderly, children, and people with a history of lung or breathing conditions, like asthma or COPD. If it’s over 150, it could be harmful for anyone. 

Since the rating on Dec, 10 was more than 150 that day, it mattered for everyone.

Dec. 10 was indeed the worst day for air quality in December. But different sources reported different numbers. According to IQAir, it was 111 AQI that day. AirNow also shows that it was at 125 AQI and “unhealthy for sensitive groups” in a narrow bubble in Southeastern Michigan. Curious said that their numbers came from morning readings on the Apple weather app. Here’s some more detail on how air quality is measured.

And that’s part of the challenge in accurately rating air quality. As we found out in our last Ask Planet Detroit entry, it’s highly dependent on proximity to the source of pollution, whether that’s a factory or freeway. Even a couple of blocks can make a big difference in how many pollutants you inhale. 

Paul Gross, a meteorologist at WDIV-TV Channel 4, says that air quality in Metro Detroit is better in the winter overall. “We generally don’t have as many stagnant weather patterns,” he says. “More fronts come through, more storm systems, more wind. That keeps the atmosphere mixed and prevents particulates from building up.”

Gross looked at the weather on Dec. 10 and found that there was “high pressure overhead and not a lot of wind, which probably helped trap the pollution.”

While those numbers are still below the “unhealthy for everyone” threshold, we should be concerned about any elevation in AQI because many Detroit residents have breathing complications due to legacy effects of poor air quality from multiple sources. Heavy industry and a high volume of automobile traffic have caused asthma rates in the city to be about 50% higher than in the suburbs. A report by the American Lung Association, as summarized by IQAir, placed Detroit’s annual particle pollution “in the top five percent of all the cities measured.”

We also learned in our last Ask Planet Detroit entry that high pollution days result in more hospitalizations. But Dr. Paul Thomas, founder of Plum Health DPC, says that a lot of people have had trouble breathing lately because of COVID-19, and the “noisy data” makes it difficult to determine if there were more incidences of lung-related issues on December 10 that could be attributable to the poor air quality that day. 

Thomas says that it’s a good idea to check the daily AQI readings, especially if you or family members have lung complications, and avoid exercising outdoors and near high vehicle traffic areas when the air quality is poor. “If you have a child with asthma,” he adds, “have a plan for asthma attacks. Make sure they know how to use a rescue inhaler and that their teachers are familiar with the symptoms of asthma.”

Gross says that on high AQI days, people are urged to use less electricity to reduce strain on power plants, carpool, and not to use gasoline-powered lawn equipment. 

Here’s more info on how we regulate air quality in Michigan, and here’s a list of our stories on air quality in Planet Detroit. A recent editorial in The Hill penned by Detroit environmental attorney Nick Leanard and Sierra Club organizer Justin Onwenu argues that our regulatory framework doesn’t do enough to account for the impact of multiple sources of air pollution within geographic areas, and that an exposure-based framework is needed to protect public health.

We know this isn’t a definite answer to your question, Curious, but hopefully, you and other readers are better informed about the significance of the AQI, and what you should do when there’s an elevated reading. 


Aaron Mondry for Planet Detroit


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