On Wednesday, Chicago residents were startled by alerts from their smartphones warning of a significant decline in air quality, with some applications even categorizing the air as “very unhealthy.”
The warnings sparked confusion among users, as contrasting information emerged from widely used air quality monitoring sites, such as AirNow.gov, which showed air quality levels as good on that day.
Despite the alarming notifications, AirNow indicated that air quality levels only rose to “moderate” by Thursday.
Google’s Abigail Jaffe clarified that the issue stemmed from inaccurate high measurements reported by a third-party monitoring station, which the company has since resolved.
According to Jaffe, Google compiles air quality information from various sources, including government monitoring stations, commercial sensor networks, and models tracking fire smoke and dust influenced by weather patterns.
As for Apple, the company has not yet responded to inquiries regarding its air quality alerts.
The Chicago Department of Public Health affirmed on Wednesday that there were no confirmed unhealthy air quality levels while acknowledging the technical glitch affecting Google and Apple’s alerts.
The department further explained the role of the Office of Emergency Management and Communications (OEMC) in coordinating city responses to emergencies, including air quality concerns, by collaborating with multiple departments.
Typically, residents would be informed when the Illinois Environmental Protection Agency (IEPA) issues an Air Quality Alert, highlighting any expected air quality levels reaching the “Unhealthy for Sensitive Groups” criterion and offering safety recommendations.
The reported air quality discrepancies occurred amid recent assessments that placed Chicago’s air quality among the worst in the nation.
The American Lung Association’s 2025 State of the Air Report revealed alarming statistics about the Chicago-Naperville metropolitan area, marking it as one of the most polluted areas in the U.S. regarding both ozone and year-round particle pollution.
According to the report, the Chicago-Naperville region advanced from 17th to 15th place nationally concerning ozone pollution and now ranks 13th in year-round particle pollution.
Inquiries into current air quality levels can be made through various online platforms, including AirNow.
For clarity, what constitutes an unhealthy air quality level? AirNow outlines that its air quality index categorizes pollution levels alongside related health risks.
If the AQI values surpass 100, air quality becomes unhealthy at first for sensitive groups, ultimately affecting everyone as the values rise further.
Once levels exceed 300, they fall into the hazardous category, which prompts immediate health concerns for the general population.
The Air Quality Index (AQI) is categorized into six distinct levels: green (good), yellow (moderate), orange (unhealthy for sensitive groups), red (unhealthy), purple (very unhealthy), and maroon (hazardous).
To provide context, what do these AQI numbers signify, and from where do they derive?
The AQI numbers do not directly reflect specific pollutant counts in the air. For example, an AQI of 300 does not indicate the presence of 300 pollutants but rather serves as a reference to convey pollution levels.
Generally, a higher AQI rating signifies greater air pollution and heightened health concerns. An AQI rating of 100 roughly corresponds to the short-term national ambient air quality standard intended to protect public health.
When AQI ratings remain at or below 100, they are typically viewed as satisfactory. However, as the ratings climb above 100, air quality becomes increasingly unhealthy—initially impacting sensitive groups, then the broader public as the figures elevate further.
The AQI scale ranges from 0 to 500, with 500 representing the most severe conditions.
The AQI evaluates five major air pollutants according to guidelines from AirNow, ensuring an accurate understanding of air quality levels and health implications.
image source from：https://www.nbcchicago.com/news/local/was-chicagos-air-quality-actually-bad-wednesday-no-heres-what-happened/3729958/
