Meghan Hodges
Chicago has a long history of unhealthy air pollution, dating back to the city's industrialization in the late nineteenth century. In 2024, Chicago was ranked as the seventh-most polluted major city in the US, and in 2025, it was ranked 13th for year-round particle pollution. The city's air quality is largely affected by vehicle emissions, power plants, manufacturing, and wildfires. In 2019, Chicago averaged an annual PM2.5 level of 12.8 μg/m3, exceeding the recommended exposure limits by the World Health Organization and the US Environmental Protection Agency (EPA). The EPA also deemed Chicago nonattainment for exceeding unhealthy air pollution days, with ozone being a key pollutant. Chicago's pollution levels vary across neighborhoods, with areas along major highways and Lake Michigan experiencing higher concentrations of nitrogen dioxide and particulate matter.
| Characteristics | Values |
|---|---|
| Air Quality Index (AQI) | 52 ("moderate") in 2019 |
| PM2.5 level | 12.8 μg/m3 in 2019 |
| Number of unhealthy ozone days | 19.2 per year in 2019 |
| Ozone pollution ranking | 16th out of 229 metropolitan areas |
| Particle pollution ranking | 13th in the US in 2025 |
| Number of days with unhealthy air pollution | 3.4 days in 2019 |
| Number of days with unhealthy ozone | 14 days in 2019 |
| Cause of increased particle pollution | Wildfire smoke |
| History of unhealthy air pollution | Yes, since the 19th century |
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What You'll Learn
Chicago's air quality is among the worst in the US
Chicago's air quality is among the worst in the United States, according to several reports. The American Lung Association's 2019 "State of the Air" report revealed that Chicago ranked as the 18th most polluted city in the nation for ozone pollution. The report also found that Chicago had experienced an average of 14 unhealthy ozone days between 2015 and 2017, a significant increase from the previous year's report. In 2024, Chicago was ranked as the 7th most polluted major US city, down from 2nd the previous year.
Chicago's air pollution problem has a long history, dating back to the city's industrialization in the late 19th century. The burning of dirty coal to power buildings, engines, and steel mills blanketed the city in a toxic cloud, leading to increased health issues such as pneumonia, asthma, and heart and lung diseases. While regulations were put in place as early as 1881, significant reductions in pollution were only achieved after World War II when coal usage began to decline.
Today, Chicago continues to struggle with air pollution, particularly with ozone and particle pollution. Ozone is a harmful gas pollutant and a key component of smog, which is formed when nitrogen oxides and volatile organic compounds react in warmer temperatures and sunlight. Chicago has been deemed ''nonattainment'' by the US EPA for exceeding the allowed number of days with unhealthy air pollution levels. In addition, the city has had difficulty complying with federal ozone standards.
Particle pollution, or fine particulate matter (PM2.5), is another major concern for Chicago. In 2019, Chicago averaged an annual PM2.5 level of 12.8 μg/m3, exceeding the recommended levels by the World Health Organization and the US EPA. This places Chicago as the worst in Illinois for particle pollution and 79th nationally out of 1517 metropolitan areas. The sources of particle pollution in Chicago include coal-fired power plants, diesel emissions, wildfires, and wood-burning devices.
The impact of poor air quality on public health is significant. According to the ALA, there are a large number of individuals with COPD, cardiovascular disease, and asthma in the area, who are particularly at risk from the effects of air pollution. Additionally, particle pollution can have serious health consequences, including triggering asthma attacks, heart attacks, strokes, and even leading to lethal outcomes. Disadvantaged and marginalized communities have historically borne the burden of poor air quality, experiencing higher concentrations of pollutants.
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Wildfire smoke is a major cause of pollution
Chicago's air quality has been ranked among the worst in the United States, and even the world, with wildfires being a significant contributor to this poor air quality. In 2023, smoke from wildfires in Canada caused very hazy conditions and plummeting air quality in Chicago, leading to air quality alerts in the city and the surrounding areas of Illinois, Indiana, and Wisconsin. Similarly, in 2025, Chicago's air quality was deemed poor and unhealthy due to smoke from wildfires in Canada.
Wildfire smoke contains microscopic contaminants known as particle pollution, which can be embedded deep in the human lungs and can be hazardous over extended periods. According to the Environmental Protection Agency, particle pollution includes solid particles and liquid droplets in the air, such as dust, dirt, soot, or smoke. Fine particulate matter, known as PM2.5, is of particular concern as these particles are fine enough to be inhaled and have diameters generally 2.5 micrometers and smaller. PM2.5 pollution in Chicago has been a persistent issue, with the city breaching both World Health Organization and US Environmental Protection Agency targets for annual PM2.5 exposure in 2019.
The impact of wildfire smoke on Chicago's air quality is not an isolated incident. The city has a long history of unhealthy air pollution, dating back to its industrialization in the late nineteenth century when the burning of dirty coal shrouded Chicago in a dense toxic cloud. While regulations to combat air pollution were implemented as early as 1881, significant pollution reductions were only realized after World War II when coal usage began to decline.
Today, Chicago continues to face air quality challenges, with the American Lung Association reporting that the Chicago-Naperville metropolitan area is one of the most polluted in the United States in terms of both ozone and year-round particle pollution. Wildfire smoke, intensified by extreme heat and drought, has been identified as a significant contributor to the increase in particle pollution. The climate crisis is driving more frequent and intense wildfires, and health officials predict that climate-driven fires may become the new normal, posing ongoing risks to air quality in Chicago and other affected regions.
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Nitrogen dioxide and particulate matter are twice as concentrated in some neighbourhoods
Chicago's air quality has been a concern for quite some time. The city has a long history of unhealthy air pollution, dating back to its industrialization in the late nineteenth century. While the city has made efforts to improve air quality, it continues to face challenges, especially with particle pollution and ozone levels.
A recent Northwestern University study found that Chicago's pollution varies significantly from neighborhood to neighborhood. The research, published in the Journal of Geophysical Research: Atmospheres, used a high-resolution simulation to estimate air quality at a neighborhood scale. By tracking three main health-hazardous pollutants: nitrogen dioxide, fine particulate matter, and ozone, the researchers gained valuable insights into the distribution of air pollution across the city.
The findings revealed that neighborhoods along major interstate highways, such as I-290, I-90, and I-94, experienced twice the concentration of nitrogen dioxide and particulate matter compared to communities with the lowest pollution levels in Chicago. This disparity in air quality has important implications for the health and well-being of residents in these areas. Nitrogen dioxide and particulate matter can have detrimental effects on both physical and mental health, increasing the risk of respiratory and cardiovascular issues.
The study also found that neighborhoods directly abutting Lake Michigan, like Cook County, experienced higher levels of ground-level ozone pollution. This discovery underscores the complex interplay between geographical location and air pollution, as ozone formation is influenced by warmer temperatures and sunlight.
Addressing this uneven distribution of air pollution is crucial to ensuring the health and equity of all Chicago communities. Decision-makers can utilize the neighborhood-scale estimates provided by the study to implement targeted solutions, such as electrifying public transit or creating more green spaces in the most affected areas.
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Chicago's air pollution is a health risk
Ozone is a harmful gas pollutant and a key component of smog, which is created when precursor pollutants, nitrogen oxides (NOx), and volatile organic compounds (VOCs) react in warmer temperatures and sunlight. Chicago has historically struggled to comply with federal ozone standards, and in 2019, the city was deemed 'nonattainment' by the US Environmental Protection Agency (EPA) for exceeding unhealthy air pollution levels.
Particle pollution, also known as soot, is another significant issue in Chicago. It is composed of tiny particles from sources such as coal-fired power plants, diesel emissions, wildfires, and wood-burning devices. These particles can lodge deep in the lungs, triggering asthma attacks, heart attacks, and strokes, and can even be lethal. Chicago ranked 13th in the country for year-round particle pollution in 2025, an improvement from its ranking of 18th in 2019, thanks to the cleanup of coal-fired power plants and the retirement of old diesel engines.
The health risks associated with air pollution in Chicago are serious. According to the American Lung Association, there are nearly 500,000 individuals with COPD, more than 600,000 with cardiovascular disease, and nearly 900,000 individuals with asthma in the area, making them particularly vulnerable to the harmful effects of poor air quality. The US Environmental Protection Agency (EPA) defines "moderate" air quality as potentially unhealthy for sensitive groups, including children, the elderly, and people with pre-existing cardiovascular or respiratory health conditions.
Additionally, a Northwestern University study found that air pollution levels vary across Chicago's neighborhoods, with communities along major interstate highways or Lake Michigan experiencing higher levels of nitrogen dioxide and particulate matter than other areas. This inequality in the distribution of air pollution highlights the need for targeted solutions, such as electrifying public transit or creating more green spaces, to protect the health and well-being of Chicago's residents.
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Chicago's air pollution is a long-standing issue
Chicago has a long history of unhealthy air pollution, dating back to the city's industrialization in the late nineteenth century. During this period, the city relied on dirty coal, which produced soot that blanketed Chicago in a dense toxic cloud, leading to an increase in instances of pneumonia, asthma, and heart and lung diseases.
As early as 1881, regulations were implemented to combat the city's air pollution problem, making Chicago one of the earliest cities to do so. However, it wasn't until after World War II, when coal usage declined, that significant reductions in pollution were achieved.
In recent years, Chicago has continued to face challenges in maintaining healthy air quality. In 2019, the city averaged an air quality index (AQI) of 52, which is considered "moderate" by the US Environmental Protection Agency (EPA). However, this level of air quality can still be potentially unhealthy for sensitive groups such as children, the elderly, and people with pre-existing cardiovascular or respiratory health conditions.
Chicago's air pollution is mainly attributed to fine particulate matter (PM2.5) and ozone. In 2019, the city exceeded both the World Health Organization (WHO) and US EPA targets for PM2.5 pollution, ranking as the worst in Illinois for particle pollution and 79th nationally out of 1517 metropolitan areas. Additionally, Chicago was deemed 'nonattainment' by the US EPA in 2019 for exceeding the number of days with unhealthy air pollution levels due to ozone.
The city's air quality has also been impacted by external factors such as wildfire smoke, which has blanketed large areas of the country, including Chicago. Climate change has contributed to the increasing severity and reach of these wildfires, making air pollution a persistent issue for the city.
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Frequently asked questions
Chicago is among the most polluted cities in the US. In 2024, it was ranked the 7th most polluted major US city, down from 2nd in 2023. In 2019, it was ranked the 18th most polluted city in the nation.
Chicago's pollution is caused by a combination of factors, including vehicle emissions, industrial activities, and wildfires. The transportation sector, power plants, and manufacturing are major sources of pollutants.
A Northwestern University study found that neighbourhoods along major interstate highways, such as I-290, I-90, and I-94, experience higher levels of pollution, particularly nitrogen dioxide and particulate matter. Neighbourhoods near Lake Michigan also experience increased ground-level ozone pollution.
Chicago's air pollution poses risks to sensitive groups, including children, the elderly, and people with pre-existing cardiovascular or respiratory conditions. The pollution can trigger asthma attacks, heart attacks, and increase the risk of lung cancer, cardiovascular damage, and other serious health issues.
Efforts are being made to address Chicago's air quality issues. The city has a long history of air pollution regulations, dating back to the 19th century. More recently, the cleanup of coal-fired power plants and the retirement of old diesel engines have helped reduce particle pollution. Additionally, potential solutions like electrifying public transit and creating more green spaces are being explored.
