Greta Jimenez
Chicago has a long history of unhealthy air pollution, dating back to the city's industrialization in the 19th century. In 2024, Chicago was ranked as the seventh-most polluted major city in the US. The city has struggled with meeting federal ozone standards, and its air quality has been deemed moderate and potentially harmful to sensitive groups. Chicago's pollution is largely attributed to vehicle emissions, industrial activities, and wildfires, which contribute to the formation of ozone and particle pollution. These pollutants have significant health impacts, including respiratory issues, cardiovascular damage, and potential lethal consequences. The city has implemented measures to address pollution, but the Trump administration's deregulation efforts may pose challenges to these improvements.
| Characteristics | Values |
|---|---|
| Air Quality Index (AQI) in 2019 | 52 ("moderate") |
| Main pollutants | Fine particulate matter (PM2.5) and ozone |
| Number of unhealthy ozone days in 2019 | 14 |
| Number of unhealthy ozone days in 2018 | 9.8 |
| American Lung Association's 'State of the Air' report ranking in 2019 | 18th most polluted city in the US |
| American Lung Association's 'State of the Air' report ranking in 2024 | 7th most polluted major US city |
| Chicago's Cook County rating by the State of the Air report from the American Lung Association | 'F' for ozone |
| Chicago's Cook County ranking by the State of the Air report from the American Lung Association | 16th for high ozone out of 229 metropolitan areas |
| US EPA rating in 2019 | 'Nonattainment' for exceeding 3.4 calendar days of unhealthy air pollution by more than 5 times with an average of 19.2 unhealthy ozone days per year |
| Chicago's contribution to smog violations in other states | Highest in the US |
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What You'll Learn
Chicago's air pollution is largely caused by vehicle emissions
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 to heat buildings, run motor engines, and power steel mills. The soot produced by burning coal covered the city in a toxic cloud, leading to increased instances of pneumonia, asthma, and heart and lung diseases. While coal usage has declined since World War II, other sources of pollution have contributed to Chicago's air quality issues.
One significant contributor to Chicago's air pollution is vehicle emissions. As a major transportation hub, Chicago experiences high volumes of road, rail, and air traffic. The suburbanization of the city and its dependence on motor vehicles have led to increasing transport emissions. These emissions include pollutants such as carbon monoxide, nitrogen oxides, and hydrocarbons, which can have harmful effects on human health and the environment. Diesel transport, including trucks and trains, are major sources of PM2.5 emissions in Chicago, followed by passenger vehicles.
To address vehicle emissions, Illinois has implemented a Vehicle Emissions Inspection Program. This program identifies malfunctioning emission control systems in vehicles and requires repairs to reduce air pollution. However, despite these efforts, Chicago continues to struggle with meeting federal attainment levels for pollution, particularly ozone levels. Ground-level ozone, or smog, is a significant issue in Chicago, especially during the summer months when temperatures are higher.
In recent years, there have been some improvements in Chicago's air quality. During the COVID-19 pandemic, lockdown measures led to a decrease in transport activity and a subsequent improvement in air quality. Additionally, the Illinois Vehicle Emissions Inspection Law of 2005 aims to reduce air pollution from motor vehicles in areas like Chicago. However, despite these efforts, Chicago still faces challenges in reducing air pollution, particularly from vehicle emissions.
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The city's industrial history has contributed to poor air quality
Chicago has a long history of poor air quality, dating back to the city's industrialization in the late nineteenth century. During this period, Chicago relied heavily on dirty coal from southern Illinois to heat buildings, power engines, and run steel mills. The soot produced by burning this coal blanketed the city in a toxic cloud, leading to increased health issues for its residents, including pneumonia, asthma, and heart and lung diseases. As a result, even as early as 1881, Chicago was one of the first cities to implement regulations to combat air pollution.
While these regulations set a precedent, significant pollution reductions were only achieved after World War II when coal usage started to decline. In 1959, the city established the Department of Air Pollution Control to further investigate and regulate emission sources. Despite these efforts, Chicago continues to struggle with air pollution, particularly with meeting federal ozone standards.
Ozone, a harmful gas and key component of smog, is formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in warmer temperatures. With Chicago's hot summers, this makes the city especially susceptible to high levels of ozone. The 2019 State of the Air report revealed that Chicago experienced 14 days of unhealthy ozone levels in 2019, an increase from 9.8 days the previous year. The report also noted that as global warming raises temperatures, ozone pollution will likely become even more prevalent.
In addition to ozone, Chicago also faces challenges with particle pollution, which includes PM2.5 and PM10. These fine particles can lodge deep in the lungs and have been linked to serious health issues, including asthma attacks, heart attacks, and even increased risk of premature death. While year-round particle pollution levels have dropped due to the cleanup of coal-fired power plants, Chicago still experiences unhealthy air quality, especially with the contribution of emissions from vehicles.
Transport emissions, including those from the widespread use of cars in the city, have further exacerbated Chicago's air pollution problem. The American Lung Association's 2019 report highlighted that Chicago residents are "breathing unhealthy air, largely caused by hotter days and vehicle emissions, placing our health and lives at risk." The report also noted that the city's air pollution worsened, ranking as the 18th most polluted city in the nation for ozone pollution, a rise from 22nd in the previous year's report.
Chicago's industrial history, particularly its reliance on dirty coal, set the stage for the city's ongoing air quality issues. While regulations and the decline of coal usage have helped, Chicago continues to face the negative impacts of pollution, affecting the health and well-being of its residents.
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Chicago's ozone pollution is worse in the summer
Chicago has a long history of poor air quality, dating back to the city's industrialization in the 19th century. While efforts to reduce pollution have been made over the years, the city continues to struggle with unhealthy levels of air pollution. In 2024, Chicago was ranked as the seventh-most polluted major city 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, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs), react in warmer temperatures and sunlight. As temperatures above 84°F are typically required for ozone formation, it is much more prevalent in the summer months.
Chicago has faced challenges in complying with federal ozone standards. In 2019, the city exceeded the allowed number of days with unhealthy ozone levels, leading to a 'nonattainment' status by the US Environmental Protection Agency (EPA). The State of the Air report from the American Lung Association gave Chicago's Cook County an 'F' rating for ozone levels, highlighting the severity of the issue.
During the summer, temperature inversions can further exacerbate ozone pollution in Chicago. These inversions occur when cool surface-level air from Lake Michigan is trapped by a warmer air layer above, preventing normal pollution dispersion. As a result, emissions linger and accumulate, leading to increased ozone formation.
The combination of temperature inversions and high emissions during the summer can have dangerous effects on human health. Sensitive groups, including children, the elderly, and people with pre-existing cardiovascular or respiratory conditions, are particularly vulnerable to the impacts of ozone pollution. It can cause throat irritation, difficulty breathing, and other health issues, leading to reduced time spent outdoors and potential long-term consequences.
Relevant sources for further information on Chicago's air pollution and real-time air quality indices include:
- IQAir
- Chicago Tribune
- Real-time air quality indices from various organizations, such as AccuWeather and AQICN.
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Chicago's air pollution is affected by wildfires
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 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, increasing instances of pneumonia, asthma, and heart and lung diseases.
While the city has made significant strides in reducing pollution since then, with pollution levels now being a small fraction of their historical levels, Chicago still struggles with unhealthy air pollution. In 2019, the city averaged an air quality index (AQI) of 52, which is considered "moderate." 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.
One factor that affects Chicago's air pollution is wildfires. For example, in 2025, smoky air from Canadian wildfires enveloped Chicago for three days, causing the city's air quality to be ranked as the worst in the United States. The tiny, airborne smoke particles from these wildfires resisted dispersal by light rain, concentrating to levels unhealthy for the general public.
Wildfires in the Canadian province of Quebec during the summer of 2023 also contributed to higher levels of fine particulate matter (PM2.5) in Chicago. PM2.5 pollution is fine particle pollution that measures 2.5 microns in diameter or less. These particles can have a range of chemical compositions and are known to be harmful to human health. While the impact of wildfires on Chicago's air quality depends on factors such as wind flow and patterns, the fires can settle particulate matter over large areas, affecting air quality in the region.
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The city's air quality is monitored by the Air Quality Index (AQI)
Chicago has a long history of unhealthy air pollution, dating back to the city's industrialization in the late nineteenth century. The burning of dirty coal to heat buildings, run motor engines, and power steel mills left the city shrouded in a toxic cloud, increasing instances of pneumonia, asthma, and heart and lung diseases.
Ozone is a harmful gas pollutant and a key component of smog, formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in warmer temperatures and sunlight. Chicago has struggled to comply with federal ozone standards, and in 2019, the city was deemed "nonattainment" by the US EPA for exceeding the allowed number of days with unhealthy ozone levels. The American Lung Association's "State of the Air" report has consistently ranked Chicago among the most polluted cities in the US for ozone pollution, with the 2019 report placing the city 18th. The report also highlighted that Chicago residents are breathing unhealthy air, largely due to vehicle emissions and hotter days, putting their health and lives at risk.
In addition to ozone pollution, Chicago also faces challenges with particle pollution, which includes PM2.5 and PM10. Wildfires, such as those in the Canadian province of Quebec in 2023, have contributed to higher levels of PM2.5 in the city. While the 2019 "State of the Air" report showed a decrease in year-round and short-term particle pollution levels, it is important to continuously monitor and address air quality issues to protect public health.
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Frequently asked questions
Chicago has a long history of unhealthy air pollution, dating back to the city's industrialization in the late nineteenth century. In 2019, the city averaged an air quality index (AQI) of 52 ("moderate"), which can be unhealthy for sensitive groups. In 2024, Chicago was ranked as the seventh-most polluted major city in the US, primarily due to fine particulate matter (PM2.5) and ozone pollution.
Chicago's pollution levels are influenced by various factors, including transport emissions, industrial activities, and climate change. The suburbanization of the city and its dependence on motor vehicles have led to increased transport emissions, including PM2.5, nitrogen oxides, and reactive organic compounds. Wildfires, such as those in Canada in 2023, can also significantly impact Chicago's air quality by increasing levels of PM2.5.
The pollution in Chicago has been linked to increased instances of respiratory and cardiovascular issues, including pneumonia, asthma, and heart and lung diseases. Ozone and particle pollution can increase the risk of premature death, lung cancer, asthma attacks, cardiovascular damage, and developmental and reproductive harm.
