4:02, Aug 6
live AQI index
|Air pollution level||Air quality index||Main pollutant|
|Good||32 US AQI||PM2.5|
|Open your windows to bring clean, fresh air indoors|
|Enjoy outdoor activities|
|Monday, Aug 3|
Good16 US AQI
|Tuesday, Aug 4|
Good19 US AQI
|Wednesday, Aug 5|
Good24 US AQI
Moderate54 US AQI
|Friday, Aug 7|
Moderate52 US AQI
|Saturday, Aug 8|
Moderate66 US AQI
|Sunday, Aug 9|
Moderate68 US AQI
|Monday, Aug 10|
Good50 US AQI
|Tuesday, Aug 11|
Moderate58 US AQI
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In 2019, Chicago’s air quality index (AQI) averaged an annual score of 52 or “moderate.” The US Environmental Protection Agency (EPA) defines “moderate” air quality as air potentially unhealthy to sensitive groups including children, the elderly, and people with pre-existing cardiovascular or respiratory health conditions.
An AQI rating is calculated by weighting 6 key criteria pollutants for their risk to health. The pollutant with the highest individual AQI becomes the ‘main pollutant’ and dictates the overall air quality index. Fine particulate matter (PM2.5) and ozone represent two of the most common ‘main pollutants’ responsible for a city’s AQI due to their high risk to human health and the weight the formula ascribes to them.
The World Health Organization (WHO) recommends that exposure to PM2.5 pollution should not exceed 10 μg/m3 annually. In 2019, Chicago averaged an annual PM2.5 level of 12.8 μg/m3, thereby breaching the WHO target for the first time since at least 2017. The Chicago area presently ranks worst in the state of Illinois for particle pollution and 79th nationally out of 1517 metropolitan areas. This ranking is slightly worse than Los Angeles (12.7 μg/m3), a city well known for its pollution challenges.
In addition to PM2.5 pollution, Chicago has also had difficulty complying with federal ozone standards. Ozone is a harmful gas pollutant and key component of smog, created when precursor pollutants, nitrogen oxides, and organic substances react in warmer temperatures and sunlight. Since temperatures over 80°F are typically required to create ozone, it’s much more prevalent in the summer than winter.
In 2019, Chicago was deemed ‘nonattainment’ by the US EPA for exceeding 3.4 calendar days of unhealthy air pollution by nearly 5 times the standard.1 The State of the Air report released by the American Lung Association gave Chicago an ‘F’ rating for ozone and found the city to rank 16th for high ozone out of 229 included metropolitan areas.
While year-over-year trends and averages provide insights into air quality levels in Chicago, real-time and forecast data should be monitored often for actionable insights to address ever-changing pollution levels. Chicago’s forecast air quality data is presented at the top of this page beneath the city overview.
Chicago has a long history of unhealthy air pollution levels dating back to the city's industrialization in the late nineteenth century. During this period, Chicago came to rely on dirty coal sourced from southern Illinois to heat buildings and run motor engines and power steel mills.2 The soot produced by burning dirty coal shrouded the city in a dense toxic cloud, increasing instances of pneumonia, asthma, and heart and lung diseases. As early as 1881, regulations were put in place to combat Chicago’s air pollution problem. Chicago was among the earliest cities to do so. While these regulations set a precedent for legislating for cleaner air, it wasn't until coal usage began to fall after World War II that more significant pollution reductions were realized.
In 1959, Chicago established the Department of Air Pollution Control to investigate and regulate emission sources. Subsequent regulations, including the federal Clean Air Act of 1970, and more recent city and state laws have helped further mitigate city-wide emissions. Today, Chicago air pollution levels are a small fraction of their historical levels.
Despite a long-term trend of improving air quality in Chicago, recent years show a worsening trend. Particle pollution has nearly doubled since 2017, rising from 6.7 μg/m3 in 2017, to 9.4 μg/m3 in 2018 and 12.8 μg/m3 in 2019.
While these year-over-year gains can’t be attributed to any specific pollution events, the suburbanization of the city and its dependence on motor vehicles have long caused transport emissions to plague Chicago’s air quality.3 In recent years, transport emissions have been on the rise. In addition to producing PM2.5, gas-powered transport also emits nitrogen oxides and reactive organic substances, precursors for ozone — another pollutant on the rise.
The 2019 State of the Air report published by the American Lung Association found that Chicago experienced 14 days of unhealthy ozone in 2019, increasing from 9.8 unhealthy days the year before.1 As global warming elevates city-wide temperatures, ozone pollution is expected to become even more prevalent.
During the COVID-19 pandemic, numerous global locations experienced improved air quality as a result of lockdown measures taken to reduce the spread of the virus. According to an analysis provided by the Chicago Tribune, air quality levels only improved by 1% in April 2020, as compared to the same period in 2019.4 Moreover, April 2020 was dirtier than the same month in 2017 and 2016. While weather can impact pollution averages and account for some differences, it is believed that diesel truck and train activity, which remained fairly consistent throughout the lockdown and pollute more on average than passenger cars, may be to blame.
The city of Chicago is the third most populous city in the United States with nearly 10 million residents. Like many large cities, transportation and the daily emissions of residents significantly contributes to Chicago’s air pollution.
Chicago is a major national hub of transport at the crossroads of the country’s rail, road, and air traffic. The Chicago area has the most federal highways and is the second most visited city in the country, with one of the busiest airports in the world (O’Hare International Airport).5,6 In recent years, transport emissions stemming from planes, trains, boats, automobiles, and locomotives have overtaken highly regulated coal as the city’s largest emission source.
Temperature inversions caused by a warm air-layer topping a cooler air-layer below can further exacerbate Chicago’s AQI levels. These weather events are not uncommon during the summer when cooler air from Lake Michigan is prevented from dispersing from under the warm air above, causing pollution to accumulate. June and July were among the most polluted months in 2019, with PM2.5 levels of 13.3 μg/m3 and 15.1 μg/m3 respectively
Take a look at Chicago’s air pollution map to discover the impact of local emission sources like domestic heating and transportation on PM2.5.
+ Article Resources
 New report: Chicago now ranked 18th most polluted city in the U.S.. (2019).
 Encyclopedia of Chicago - air quality. (2020).
 Milando C, et al. (2017). Trends in PM2.5 emissions, concentrations and apportionments in Detroit and Chicago.
 Hawthorne M. (May 4, 2020). Many cities around the globe saw cleaner air after being shut down for COVID-19. But not Chicago.
 Manners-Bell J. (2017). Introduction to global logistics: delivering the goods.
 Annual traffic data – 2015 Preliminary. (2020).