It's ok, Chicago, your air was actually fine on Wednesday

Chicago Tribune

24-04-2025

Readings from several popular weather apps had people across Chicago spending much of Wednesday wondering whether their air was safe to breathe — until the dangerously unhealthy levels were revealed to be a glitch.
Early in the morning, Google's air quality map showed that Chicago had the worst air in the country. Apple's weather app, too, showed that the Air Quality Index had climbed into the 400s, a reading so hazardous that people are encouraged to stay indoors. (The Air Quality Index, which ranges from 0 to 500, is a measure of the density of five pollutants in the air: ground-level ozone, particulates, carbon monoxide, nitrogen dioxide and sulfur dioxide.)
To put that in perspective, that's as high as the levels reached in 2023 when smoke from wildfires in Canada blanketed much of the East Coast and turned the sky in New York City orange.
At those levels, people are advised to stay indoors, and Madeline Blair, 24, did just that. She checked her Apple weather app when she woke up and, seeing unhealthy air quality levels, skipped her morning walk. Blair instead headed down into her basement to retrieve her air filter.
'I live on the northwest side, and my area on the map was dark purple on the Apple radar, so I'm like, No thanks, I'm just staying inside,' Blair said. (That color would indicate the air quality is at hazardous levels.)
Savannah Bhojwani, 26, who lives in Old Town, was also alarmed by the air quality readings. She saw them in the 200s at 10 a.m. on her Apple Weather app before watching them climb into the 400s later on.
She said she had thought the readings might be inaccurate, but cloudy, gray weather in the morning made it difficult to tell whether the air was polluted. She closed her windows and texted screen shots of the dangerous air quality readings to her friends. One blamed a garage fire, and another thought there might be a gas leak. Nothing pointed to the type of air quality levels that were being reported, and they couldn't find any information on the local news or from public health officials.
Similar conversations unfolded across social media, where people spent much of the day speculating about potential causes. An explosion in Indiana, as one person on Reddit suggested? Really — really — bad pollen?
The readings arrived just as the American Lung Association issued its annual State of the Air report, which suggests that even days with good air quality in Chicago may be hard on the lungs. It ranked the Chicago area 15th worst in the nation for ozone pollution, with Los Angeles at No. 1.
Not everyone was reporting the dangerous air quality levels, though. The Environmental Protection Agency's AirNow is a go-to source for air quality data and uses high-quality sensors that are closely monitored. On Wednesday, it showed good air quality in Chicago.
PurpleAir is also widely popular. Its sensors are less precise — but there are many more of them. Its map often shows air quality levels that are poorer than those on AirNow, but on Wednesday it, too, mostly reported good levels.
The Chicago Department of Public Health confirmed that the air quality index in Chicago was at safe levels Wednesday, though it declined to speculate on what might have caused the glitch in some apps. A spokesperson said that when the air quality in the city reaches unhealthy levels, the city works to assist residents and particularly vulnerable populations.
Both Apple and Google use the same source for their data: BreezoMeter, a startup acquired by Google in 2022. The company says it uses many of the same sensors as AirNow and PurpleAir but also incorporates additional data sources in determining the Air Quality Index. Late Wednesday, Abigail Jaffe, a spokesperson for Google, said the mistakenly high readings were the fault of 'a third-party monitoring station inaccurately reporting high measurements.'
By around 5 p.m. local time, both Google's and Apple's maps finally showed good air quality in Chicago.
Until then, with the Apple weather app was still showing unhealthy air but the sun finally coming out, Bhojwani decided it had all been a fluke. She has previously lived in Los Angeles — where, she said, she learned a dusty color around the sun was an indication that the air was polluted. She didn't see that in Chicago. 'This is clearly inaccurate, I thought,' she said.
Blair came to the same conclusion. 'Now it's beautiful outside — I'm about to go get coffee with a friend before going to a poetry reading,' she said just before 4 p.m. local time. 'So I guess you could say I'm resuming normal activities.'
This article originally appeared in The New York Times.