Chicago's Air Pollution: What's The Real Damage?

Chicago has a long history of unhealthy air pollution, dating back to the city's industrialization in the late nineteenth century. The city's air quality index (AQI) has been ranked as moderate by the US Environmental Protection Agency (EPA), with an average of 8.4 micrograms of particulate matter per cubic meter of air in 2024. Chicago's main pollutants include fine particulate matter (PM2.5) and ozone, which are harmful to public health and can increase the risk of serious health issues such as asthma, lung cancer, and cardiovascular damage. While Chicago has implemented initiatives to improve air quality, such as increasing the accessibility of biking for commuting, the city still faces challenges in complying with federal ozone standards.

Chicago's air pollution history

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 this coal covered Chicago in a dense toxic cloud, leading to increased instances of pneumonia, asthma, and heart and lung diseases.

As early as 1881, regulations were put in place to combat the city's air pollution problem, making Chicago one of the first cities to do so. In 1959, the city established the Department of Air Pollution Control to investigate and regulate emission sources. The federal Clean Air Act of 1970 and more recent city and state legislation have also helped to further mitigate emissions.

Despite these efforts, Chicago continues to struggle with air pollution. In 2019, the city averaged an air quality index (AQI) of 52, which is considered "moderate" by the US Environmental Protection Agency (EPA). This means that the air is potentially unhealthy for sensitive groups, including children, the elderly, and people with pre-existing health conditions. Fine particulate matter (PM2.5) and ozone are the two most common main pollutants responsible for Chicago's AQI.

Chicago's PM2.5 pollution ranks the worst in the state of Illinois and 79th nationally out of 1517 metropolitan areas in the United States. The city has also had difficulty complying with federal ozone standards. In 2019, Chicago was deemed 'nonattainment' by the US EPA for exceeding unhealthy air pollution levels. The State of the Air report from the American Lung Association found that Chicago experienced 14 days of unhealthy ozone in 2019, up from 9.8 unhealthy days the year before.

In recent years, transport emissions have been on the rise in Chicago, contributing to the worsening trend of particle pollution. The suburbanization of the city and its dependence on motor vehicles have negatively impacted air quality. While Chicago's air pollution levels are a small fraction of their historical levels, the city still has work to do to improve the air quality and protect the health of its residents.

Chicago's air quality index

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 this coal shrouded Chicago in a dense toxic cloud, increasing instances of pneumonia, asthma, and heart and lung diseases.

In 1881, Chicago was among the first cities to implement regulations to combat air pollution. In 1959, the city 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 legislation, have helped further mitigate emissions.

Despite these efforts, Chicago still struggles with unhealthy air pollution levels. In 2019, the city averaged an air quality index (AQI) of 52, which is considered "moderate" by the US Environmental Protection Agency (EPA). This means the air is potentially unhealthy for sensitive groups, including children, the elderly, and people with pre-existing cardiovascular or respiratory health conditions. Fine particulate matter (PM2.5) and ozone (O3) are the two most common main pollutants responsible for Chicago's AQI.

PM2.5 pollution is fine particle pollution with a range of chemical compositions that measure 2.5 microns in diameter or less. In 2019, Chicago was deemed 'nonattainment' by the US EPA for exceeding unhealthy air pollution levels with an average of 19.2 unhealthy ozone days per year. Chicago's PM2.5 pollution ranks worst in the state of Illinois and 79th nationally out of 1517 metropolitan areas in the United States. This ranking places Chicago air quality in a slightly worse position than Los Angeles, a city well known for its pollution challenges.

In 2024, Chicago was ranked as the seventh-most polluted major city in the US, down from second place the previous year. On average, the city's atmosphere had 8.4 micrograms of particulate matter per cubic meter of air in 2024, considerably lower than the 2023 average of 13 micrograms. However, this is still far from the World Health Organization's recommended guideline of 5 micrograms per cubic meter.

While Chicago has made significant improvements in reducing air pollution, with levels now being a small fraction of their historical levels, the city continues to face challenges in maintaining healthy air quality for its residents, especially sensitive groups.

Particulate matter in Chicago's air

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 this process shrouded Chicago in a dense toxic cloud, leading to increased instances of pneumonia, asthma, and heart and lung diseases.

Since then, the city has made significant strides in improving air quality. Regulations to combat air pollution were put in place as early as 1881, and in 1959, Chicago established the Department of Air Pollution Control to investigate and regulate emission sources. The implementation of the federal Clean Air Act in 1970 and other recent city and state legislation have further helped to reduce emissions.

Despite these efforts, Chicago still faces challenges with air pollution, particularly with particulate matter. In 2022, an analysis of readings from newly installed air sensors across the city found that areas like Little Village, Austin, Englewood, Auburn Gresham, Irving Park, and Avondale had the highest levels of particulate matter pollution, posing serious health risks to residents. These fine particles, known as PM2.5, can be as small as 2.5 micrometers in diameter or less, making them a fraction of the diameter of a human hair. They can lodge deep in the lungs and contribute to various health problems, including heart and lung disease and asthma.

The sources of particulate matter pollution in Chicago are diverse. One significant contributor is transport emissions, with the city's growing dependence on motor vehicles. Wildfires, such as those in the Canadian province of Quebec during the summer of 2023, can also impact Chicago's air quality by releasing giant migrating plumes that settle over large areas. Additionally, the suburbanization of the city and its industrial activities continue to play a role in the complex issue of particulate matter pollution.

While Chicago's air quality has improved over the years, with the frequency of unhealthy PM2.5 days falling by 97% between 2000-2002 and 2006-2008, more recent data from 2024 shows that the city ranked as the seventh-most polluted major city in the United States. The average annual concentration of small particulate matter in the air led to a 35% decrease in air pollution levels compared to the previous year, but it still exceeded the World Health Organization's recommended guideline of 5 micrograms per cubic meter.

Chicago's ozone pollution

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 burning of dirty coal to heat buildings, run motor engines, and power steel mills shrouded the city in a dense toxic cloud, increasing instances of pneumonia, asthma, and heart and lung diseases. While great strides have been made in the last few decades to improve air quality, Chicago still ranks among the most polluted cities in the United States. In 2024, it was ranked the 7th most polluted major US city, and in 2019, it was ranked the 18th most polluted city in the nation for ozone pollution.

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. Since temperatures above 84°F are typically required for ozone formation, it is much more prevalent in the summer than in the winter. Chicago's location in the Midwest on the shore of Lake Michigan makes the city prone to temperature inversions, where cool surface-level air becomes trapped by a warmer air layer above, preventing normal pollution dispersion. Marine inversions often occur in the summer when cool ground-level air is created by wind blowing in from Lake Michigan, further contributing to ozone formation.

The 2019 State of the Air report by the American Lung Association found that Chicago experienced 14 days of unhealthy ozone levels in 2019, up from 9.8 unhealthy days the year before. Chicago was deemed 'nonattainment' by the US EPA in 2019 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. The State of the Air report from the American Lung Association gave Chicago's Cook County an 'F' rating for ozone, and the county was found to contribute more to smog violations in other states than any other county.

Ozone pollution in Chicago is expected to become even more prevalent due to the effects of climate change, which has led to rising temperatures and prolonged ozone seasons. Warmer temperatures brought about by climate change make ozone more likely to form and harder to dissipate. Additionally, the suburbanization of the city and its dependence on motor vehicles have resulted in increased transport emissions, which contribute to ozone formation. While global lockdown measures during the COVID-19 pandemic resulted in improved air quality worldwide, the overall trend in Chicago indicates an increase in unhealthy ozone days.

Efforts to improve Chicago's air quality

Chicago has a long history of unhealthy air pollution dating back to the city's industrialization in the late nineteenth century. At that time, the burning of dirty coal to heat buildings, power engines, and run steel mills caused a toxic cloud of soot to hang over the city, leading to increased health issues for residents. While great strides have been made since then, with air pollution levels now only a fraction of historical levels, Chicago still faces significant challenges in improving its air quality.

One of the main sources of pollution in Chicago is transportation. The city's suburbanization and reliance on motor vehicles have led to rising transport emissions, with diesel trucks and trains contributing significantly to the problem. To address this, Chicago has implemented initiatives to reduce vehicle emissions, such as the Diesel Retrofit Program, which includes new clean diesel requirements, and idling reduction measures for diesel vehicles. The city is also encouraging the use of alternative fuels, such as compressed natural gas, E85, propane, and biodiesel, as cleaner alternatives to traditional gasoline.

In addition, Chicago is promoting sustainable modes of transportation, such as biking. The city has increased the accessibility and attractiveness of biking by constructing and maintaining 117 miles of on-street bike lanes. These efforts are supported by the Chicago Metropolitan Agency for Planning (CMAP), which provides funding for transportation projects that reduce emissions and improve air quality, including public transit, cleaner trains, and additional bike paths. CMAP also encourages communities to reduce air pollution by supporting public transit, biking, walking, and the use of electric vehicles.

Another critical aspect of Chicago's air quality improvement efforts is addressing industrial emissions. The city has established permitting and inspection processes for high-emitting industries, and it continues to monitor and regulate emission sources through its Department of Air Pollution Control. Additionally, the city has implemented clean air legislation, contributing to a significant reduction in unhealthy ozone and PM2.5 days over the past few decades.

While Chicago has made notable progress in improving its air quality, there is still work to be done. The city's air pollution levels remain “unhealthy” by EPA standards, and particle pollution continues to be a concern, with Chicago ranking 79th nationally out of 1517 metropolitan areas for PM2.5 pollution. Wildfires, such as those in the Canadian province of Quebec during the summer of 2023, also contribute to higher levels of PM2.5 pollution in the city. Nevertheless, with continued efforts and initiatives, Chicago is striving to create a healthier and more sustainable environment for its residents.

Frequently asked questions