Chicago's Air Pollution: Causes And Concerns

Chicago, the third most populous city in the United States, has been ranked as one of the most polluted cities in the nation. The city's poor air quality is caused by a range of factors, including transportation emissions, industrial activity, and temperature inversions. The Chicago area has a dense network of highways and is a major hub for road, rail, and air traffic, contributing significantly to the city's air pollution. In addition, the city's particle pollution, which includes soot, dirt, and smoke, has been attributed to power plants, diesel emissions, and industrial activity. Warmer temperatures caused by climate change also play a role in increasing ozone levels, which can have harmful effects on human health.

Ground-level ozone pollution

Ground-level ozone, also known as tropospheric ozone, is a harmful air pollutant and a key component of smog. It is formed when precursor pollutants, nitrogen oxides (NOx) and volatile organic compounds (VOCs), react in warmer temperatures and sunlight. This typically occurs when emissions from cars, power plants, industrial boilers, refineries, chemical plants, and other sources chemically react in the presence of sunlight. Ground-level ozone is of particular concern in urban areas, as it can reach unhealthy levels on hot sunny days, posing risks to human health, especially for children, the elderly, and individuals with lung diseases such as asthma.

Chicago, the third most populous city in the United States, faces significant challenges with ground-level ozone pollution. In 2019, the city was ranked as the 18th most polluted city in the nation for ozone pollution by the American Lung Association, a decline from its ranking of 22nd in the previous year's report. Chicago's ozone levels have been impacted by rising temperatures due to climate change, making it more challenging to mitigate this issue.

Transportation emissions play a significant role in Chicago's ground-level ozone pollution. The city is a major national hub for transport, with the most federal highways and one of the busiest airports in the world (O'Hare International Airport). Emissions from planes, trains, automobiles, and other vehicles contribute to the formation of ground-level ozone. Additionally, Chicago's location on the shore of Lake Michigan makes it prone to temperature inversions, where cooler air from the lake becomes trapped under a warmer air layer, hindering the dispersion of pollutants.

To address ground-level ozone pollution, the U.S. Environmental Protection Agency (EPA) has designated areas as ""attainment" or "nonattainment" based on their compliance with national ambient air quality standards. Chicago has struggled to meet these federal attainment levels. To improve air quality, states with nonattainment areas must develop a state implementation plan (SIP) outlining measures to reduce emissions and improve ozone levels. These efforts are crucial to protect the health and well-being of Chicago's residents, especially those vulnerable to the harmful effects of ground-level ozone pollution.

It is important to note that while ground-level ozone is harmful, stratospheric ozone, found in the upper atmosphere, is beneficial as it forms a protective layer that shields the Earth from ultraviolet radiation from the sun.

Particle pollution

Chicago, with nearly 10 million residents, is the third most populous city in the United States. Its particle pollution is influenced by its role as a major transportation hub, with federal highways, rail, road, and air traffic contributing to emissions. The Chicago area has the most federal highways and is the second-most visited city in the country, with O'Hare International Airport being one of the busiest airports in the world. Transport emissions from planes, trains, boats, automobiles, and locomotives have become a significant source of particle pollution in the city.

In addition to transport, particle pollution in Chicago is also attributed to industrial sources and power plants. Certain neighbourhoods, particularly on the South and West Sides, are disproportionately affected by air pollution due to their proximity to major highways and high concentrations of industry. Chicago's West Side, including North and South Lawndale, East Garfield Park, Archer Heights, and Brighton Park, experiences up to 32% higher concentrations of nitrogen dioxide (NO2) pollution compared to the rest of the city. This area also has a higher proportion of Black, Hispanic, and Latinx residents, highlighting the environmental inequities in the city.

While there has been progress in reducing year-round particle pollution, with Chicago recording its lowest levels in 2019, short-term spikes in particle pollution continue to be a concern. These spikes can be extremely dangerous and even deadly, and Chicago ranked 73rd worst in the nation for short-term particle pollution in the 2024 "State of the Air" report. Efforts to mitigate particle pollution include supporting public transit, biking, walking, and electric vehicles, as well as implementing air pollution rules and stronger national limits on ozone pollution.

Transport emissions

Chicago is a major transport hub, with a vast network of roads, rail, and air traffic. The Chicago area has the most federal highways of any US city and is the second most visited, with one of the world's busiest airports, O'Hare International. With nearly 10 million residents, it is the third most populous city in the United States. All of this contributes to a significant amount of transport emissions, which are now the city's largest emission source, overtaking highly regulated coal emissions.

The Chicago Department of Public Health (CDPH) has identified that certain neighbourhoods are disproportionately affected by air pollution, with the South and West Sides of the city bisected by major highways and high concentrations of industry. Chicago's West Side, including North and South Lawndale, East Garfield Park, Archer Heights, and Brighton Park, experiences up to 32% higher concentrations of nitrogen dioxide (NO2) air pollution compared to the rest of the city. These areas have more Black, Hispanic, and Latinx residents, highlighting the environmental inequities in the city.

To improve air quality and reduce the impact of transport emissions, Chicago can encourage the use of public transit, biking, walking, and electric vehicles. The Chicago Metropolitan Agency for Planning (CMAP) provides funding for such initiatives through the Congestion Mitigation and Air Quality Improvement Program and the Transportation Alternatives Program.

Racial and economic disparities

Chicago, the third most populous city in the United States, has been ranked as one of the most polluted cities in the nation. The city's air quality has been deemed moderate by the US Environmental Protection Agency (EPA), indicating that the air is potentially unhealthy for sensitive groups, including children, the elderly, and those with pre-existing health conditions.

The Chicago Department of Public Health (CDPH) has recognized the need to address these disparities and has committed to health and racial equity through initiatives like Healthy Chicago 2025. By analyzing community-level data on air quality, health, and social factors, the CDPH aims to identify neighborhoods that should be prioritized for mitigation and reduction of air pollution, ensuring that environmental justice is upheld for all Chicago residents.

Furthermore, transportation emissions play a significant role in Chicago's air pollution. The city is a major transport hub, with the most federal highways and one of the busiest airports in the world. Temperature inversions, caused by warm air trapping cooler air from Lake Michigan, can exacerbate pollution levels, particularly during the summer months. Disadvantaged communities located near major highways or industrial areas are at an increased risk of exposure to pollutants, further exacerbating the disparities.

To address these issues, Chicago has implemented initiatives to reduce air pollution and promote sustainable transportation. The Chicago Metropolitan Agency for Planning (CMAP) provides funding for projects that encourage public transit, biking, walking, and the use of electric vehicles. These initiatives aim to not only improve air quality but also to reduce the disproportionate impact of pollution on vulnerable communities, ensuring a healthier and more equitable environment for Chicago's residents.

Power plants and industry

Power plants and industrial buildings are major contributors to air pollution in Chicago. The city's power plants emit harmful pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOCs), which react with heat and sunlight to form ground-level ozone smog. This toxic gas is a key component of smog and can cause serious health issues, including respiratory problems and compromised lung function.

Particulate matter, which includes dirt, dust, soot, and smoke, is another significant pollutant stemming from power plants and industry. These tiny particles, measuring less than 10 micrometers in diameter, can be inhaled and penetrate deep into the lungs, and even the bloodstream. Prolonged exposure to particulate matter has been linked to adverse health effects, including asthma attacks, heart attacks, and strokes.

Chicago's industrial sectors, particularly on the South and West Sides, have been identified as hotspots for air pollution. The western edge of the city, including neighbourhoods like North and South Lawndale, East Garfield Park, Archer Heights, and Brighton Park, experiences up to 32% higher concentrations of nitrogen dioxide (NO2) pollution compared to the rest of Chicago. This disparity highlights the disproportionate impact of pollution on communities of colour, as these areas have a higher percentage of Black, Hispanic, and Latinx residents.

While efforts have been made to improve air quality, such as the cleanup of coal-fired power plants and the retirement of old diesel engines, the city continues to struggle with meeting air quality standards. The "State of the Air" report by the American Lung Association consistently ranks Chicago as one of the most polluted cities in the nation for ozone and particle pollution, underscoring the urgent need for further improvements in air quality management.

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