Chicago's Air Pollution: A Serious Concern?

Chicago has a long history of unhealthy air pollution, dating back to the city's industrialization in the late nineteenth century. In 2019, the American Lung Association's State of the Air report revealed that Chicago ranked as the 18th most polluted city in the US for ozone pollution. In 2024, Chicago was ranked the 7th most polluted major US city, down from 2nd in 2023. The city's air quality has been attributed to various factors, including wildfires, vehicle emissions, and industrial activities. With a history of pollution and ongoing challenges, Chicago's air quality remains a significant concern for its residents.

Chicago's air quality is deemed moderate with an AQI of 52

Chicago's air quality has been a concern for quite some time, with a history of unhealthy air pollution dating back to the city's industrialization in the late nineteenth century. While the city has made efforts to improve its air quality, it still faces challenges.

In 2019, Chicago's air quality index (AQI) averaged 52, which is considered "moderate" by the US Environmental Protection Agency (EPA). This means that the air quality is potentially unhealthy for sensitive groups, including children, the elderly, and people with pre-existing cardiovascular or respiratory health conditions. The AQI rating is calculated by weighting six key criteria pollutants for their risk to health, with fine particulate matter (PM2.5) and ozone being two of the most common main pollutants responsible for a city's AQI.

Chicago's PM2.5 levels in 2019 averaged 12.8 μg/m3, exceeding the recommendations of the World Health Organization (WHO) and the US EPA. This level of PM2.5 pollution ranked Chicago as the worst in the state of Illinois for particle pollution and 79th out of 1517 metropolitan areas in the US. The city has also struggled to comply with federal ozone standards, with the American Lung Association's 2019 "State of the Air" report ranking Chicago as the 18th most polluted city in the US for ozone pollution.

While Chicago's air quality is deemed moderate with an AQI of 52, it is important to recognize that the city has a history of air pollution issues and continues to face challenges in meeting federal air quality standards. The high levels of PM2.5 and ozone pollution can pose risks to the health of its residents, particularly sensitive groups. As such, it is crucial for Chicago to continue monitoring and improving its air quality to ensure the well-being of its citizens.

The air pollution is attributed to high ozone levels

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 burning dirty coal to heat buildings, run motor engines, and power steel mills. The soot produced by burning dirty coal covered the city in a dense toxic cloud, leading to an increase in instances of pneumonia, asthma, and heart and lung diseases.

While air quality has improved since then, Chicago still struggles with high levels of air pollution. In 2019, the city averaged an annual PM2.5 level of 12.8 μg/m3, exceeding the World Health Organization's target of 10 μg/m3 and the US EPA's target of 12 μg/m3. This level of PM2.5 pollution ranked Chicago as the worst in Illinois and 79th nationally out of 1517 metropolitan areas in the United States.

Ozone is a significant contributor to Chicago's air pollution problem. Ozone is a harmful gas pollutant and a key component of smog. It is created when precursor pollutants, nitrogen oxides (NOx), and volatile organic compounds (VOCs) react in warmer temperatures and sunlight. Gas-powered transport, such as cars, trucks, and trains, emit nitrogen oxides and reactive organic substances, which are precursors to ozone formation. As such, the suburbanization of the city and its dependence on motor vehicles have negatively impacted Chicago's air quality.

In 2019, Chicago was deemed 'nonattainment' by the US EPA for exceeding the allowed number of days with unhealthy air pollution. The city experienced an average of 19.2 unhealthy ozone days per year, with the American Lung Association's State of the Air report giving Chicago's Cook County an 'F' rating for ozone. Chicago ranked 16th for high ozone out of 229 metropolitan areas included in the report and was the 18th most polluted city in the nation for ozone pollution.

The impact of high ozone levels on public health is significant. Both ozone and particle pollution can increase the risk of premature death and other serious health issues, including lung cancer, asthma attacks, cardiovascular damage, and developmental and reproductive harm. Warmer temperatures brought about by climate change further exacerbate the problem, as ozone is more likely to form and is harder to clean up in these conditions.

Chicago's air pollution is worse than Los Angeles's

Los Angeles, on the other hand, is known for its smog, a combination of particle and ozone pollution. The city's air pollution is primarily due to the burning of fossil fuels, especially by vehicles, ships, planes, and manufacturing, as well as wildfires. While Los Angeles has made significant improvements in reducing air pollution over the last 30 years, it still does not meet the US EPA's national air quality standards for PM2.5 and ozone.

Chicago's air pollution has been a concern since the city's industrialization in the late 19th century, when it relied heavily on dirty coal, which increased instances of pneumonia, asthma, and heart and lung diseases. Today, Chicago continues to rank among the worst in the nation for air pollution. In 2025, the metro area ranked 15th overall for levels of smog, which is worse than the previous two yearly reports. Chicago also ranked 19th in the nation for annual average pollution by fine particles.

While both cities struggle with air pollution, Chicago's PM2.5 pollution is worse than Los Angeles's. Chicago's PM2.5 concentration is currently 1.4 times the World Health Organization's annual guideline value, and in 2019, it averaged an annual PM2.5 level of 12.8 μg/m3, breaching both WHO and US EPA targets. In addition, Chicago has had difficulty complying with federal ozone standards, with an average of 19.2 unhealthy ozone days per year.

To address Chicago's air pollution problem, the lung association director, Kristina Hamilton, recommends reducing diesel pollution, truck and freight traffic, and emissions from these sources. Chicago's real-time air quality data is available through various online platforms, such as IQAir and AirVisual, and users can also install air quality plugins and widgets on their browsers and desktops to stay informed about the city's air pollution levels.

The city's industrial past is a contributing factor

Chicago's air quality has been a persistent issue, with the city's industrial past being a significant contributing factor. The city's history of unhealthy air pollution dates back to the late 19th century during its rapid industrialization. Chicago became heavily dependent on dirty coal, which was used for heating buildings, powering engines, and operating steel mills. The combustion of this low-quality coal released vast amounts of soot and toxic pollutants into the atmosphere, creating a dense cloud that enveloped the city. This soot consisted of fine particles, primarily PM2.5, which are known to have detrimental effects on human health.

The consequences of this pollution were severe, leading to increased instances of pneumonia, asthma, and heart and lung diseases among the populace. Recognizing the urgency of the situation, Chicago was among the first cities to implement regulations to combat air pollution as early as 1881. However, it wasn't until after World War II, when coal usage began to wane, that Chicago witnessed more significant improvements in air quality.

Despite these historical efforts, Chicago continues to face air pollution challenges today. In 2019, the city experienced a spike in air pollution, with an annual PM2.5 level of 12.8 μg/m³, exceeding both World Health Organization and US EPA targets. This level of fine particle pollution ranked Chicago as the worst in Illinois and 79th out of 1517 metropolitan areas nationwide. The same year, the American Lung Association's "State of the Air" report ranked Chicago as the 18th most polluted city in the US for ozone pollution, with an average of 14 unhealthy ozone days between 2015 and 2017.

Ozone, a key component of smog, is formed when precursor pollutants, nitrogen oxides (NOx), and volatile organic compounds (VOCs) react in warmer temperatures and sunlight. Chicago's hot summer days contribute to the formation of ozone, making it a persistent issue for the city. In 2019, the US EPA deemed Chicago 'nonattainment' due to exceeding the allowed number of days with unhealthy air pollution levels.

While Chicago's air quality has shown some improvement, with a decrease in the average annual concentration of small particulate matter in 2024, it still ranked as the 7th most polluted major US city in the same year. This ranking underscores the ongoing air quality challenges faced by the city. Factors such as wildfires and emissions from vehicles and industrial sources continue to impact Chicago's air quality, highlighting the complex nature of addressing pollution in the city.

Climate change is worsening air quality

Chicago has a long history of unhealthy air pollution, dating back to the city's industrialization in the late nineteenth century. While the city has made efforts to improve its air quality, it continues to face challenges. In 2019, Chicago averaged an Air Quality Index (AQI) of 52, which is considered "moderate." However, this still poses potential health risks to sensitive groups such as children, the elderly, and people with pre-existing health conditions.

Climate change is indeed worsening air quality, not just in Chicago but in many regions across the globe. Here are some ways in which climate change is impacting air quality:

• Ground-level ozone: Warmer temperatures associated with climate change increase ground-level ozone, a harmful gas pollutant and a key component of smog. Ozone is formed when precursor pollutants, nitrogen oxides (NOx), and volatile organic compounds (VOCs) react in warmer temperatures and sunlight. Higher temperatures lead to more frequent and intense heat waves, which further contribute to increased ozone formation.
• Particulate matter: Climate change-induced droughts, forest fires, and dust storms can increase particulate matter in the air, degrading air quality. Fine particle pollution, known as PM2.5, can have adverse health effects, especially for sensitive groups.
• Allergens: A changing climate leads to earlier and longer springs and summers, causing higher pollen concentrations and longer pollen seasons. Increased airborne allergens, such as pollen, can trigger allergy-related illnesses like asthma and hay fever.
• Indoor air quality: Climate change can also impact indoor air quality. Higher levels of outdoor pollutants can enter buildings through doors, windows, and ventilation systems, affecting the health of occupants, especially those with pre-existing respiratory or heart conditions.

The effects of climate change on air quality vary by region, and areas with poor air quality may experience further deterioration due to climate change. It is important to monitor real-time and forecast data to address the ever-changing pollution levels and implement effective measures to mitigate the impacts of climate change on air quality.

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