Northwestern model finds elevated air pollution over Lake Michigan and Chicago’s interstates

Scientists say pollution levels were highest over Lake Michigan, lakeside neighborhoods and areas near interstate highways.

Chicago air pollution
A thick haze of smog looms over the Chicago skyline in this 2015 file photo. Nam Y. Huh / Associated Press
Chicago air pollution
A thick haze of smog looms over the Chicago skyline in this 2015 file photo. Nam Y. Huh / Associated Press

Northwestern model finds elevated air pollution over Lake Michigan and Chicago’s interstates

Scientists say pollution levels were highest over Lake Michigan, lakeside neighborhoods and areas near interstate highways.

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Recently published research from Northwestern University identifies Chicago’s air pollution hotspots, shedding light on its disproportionate impact across the city.

The study – published last month in the Journal of Geophysical Research: Atmospheres – found that neighborhoods near interstate highways and Lake Michigan experience a higher concentration of air pollution than others.

The research shows that levels of ozone are highest over Lake Michigan, so lakeside neighborhoods experience the most ground level ozone. Ozone is a secondary chemical: it forms from nitrogen oxides and volatile organic compounds in the presence of sunlight. Lake breezes carry these pollutants from the city out over the water, where they form ozone.

Researchers also found that neighborhoods next to interstates – like I-290, I-90 and I-94 – experience the highest levels of some types of air pollution. These neighborhoods see twice the concentration of pollutants compared to areas with the lowest pollution levels in Chicago.

Northwestern scientists used mathematical equations to simulate chemical and physical reactions. They pulled emissions data from the U.S. Environmental Protection Agency, and also looked at building types, land cover and weather conditions.

They brought it together to form a high resolution computer model that can track hour-by-hour levels of nitrogen dioxide, ozone and particulate matter 2.5 – a type of pollution made up of tiny bits of contaminants and chemicals. The model reveals pollution across blocks of space as small as nearly one mile (1.3 kilometers).

Northwestern said this simulation is the first to show neighborhood-scale pollution in the Chicago area by combining chemical models and high resolution emissions data.

NU Chicago pollution maps
These maps of Chicago show levels of pollution for, from left to right: nitrogen dioxide, ozone and particulate matter 2.5. The lines inside the maps represent interstate highways. Source: Anastasia Montgomery, Northwestern University

While the U.S. Environmental Protection Agency is required by the Clean Air Act to monitor these pollutants, active sensors around Chicago are sparsely distributed. These sensors don’t capture the whole picture, said Anastasia Montgomery, a Ph.D student in Northwestern’s Department of Earth and Planetary Sciences and lead author of the study.

She said the difference in pollution levels between neighborhoods doesn’t get picked up by a few monitors placed over large distances, but Northwestern’s high resolution tool can fill in those gaps.

“Our estimate of what’s happening in the space between monitors is based on what we know about physics, chemistry and emissions, rather than just assuming the values are going to be an average of what the monitors say,” Montgomery explained. “This means that we’re able to capture areas with high pollution that the monitors do not observe.”

An analysis done last year by WBEZ, the Chicago Sun-Times and MuckRock identified air pollution hotspots in Englewood, Little Village, Austin, Irving Park, Avondale and Auburn-Gresham using data from 94 Microsoft sensors installed around the city.

The story noted that even 100-plus sensors were not nearly enough to cover the whole city – and that inhibits further analysis of the Southeast and Far South Sides, areas that are known to be heavily impacted by air pollution.

Montgomery also said the tool can simulate how air pollution might change due to weather patterns or new policies targeting pollution.

“We can ask the model to show us how the same time period may look with a specific policy in place,” she said. “We can simulate the same week, pre- and post-policy, and be smart about the choices we make about air pollution.”

Jose Acosta-Cordova, the senior transportation policy analyst with the Little Village Environmental Justice Organization, said diesel truck emissions are a big contributor to these levels.

“When you think about how many heavy duty diesel trucks are coming through the Chicago area every day, it’s not surprising at all, right? And the majority of them are taking those highways,” Acosta-Cordova said.

Particulate matter 2.5 and nitrogen dioxide are associated with industrial and vehicular emissions. Chicago is a major freight and trucking hub: according to the Chicago Metropolitan Agency for Planning, trucks account for about one in seven vehicles on Illinois’ urban interstates.

Montgomery and Acosta-Cordova stressed the detrimental health effects of these pollutants. Ozone, particulate matter 2.5 and nitrogen dioxide have been linked to asthma, respiratory infections and premature death – and are especially harmful for children, the elderly and people with pre-existing conditions.

The city of Chicago’s 2020 Air Quality and Health report estimated that 5% of premature deaths in the city each year can be linked to particulate matter 2.5 exposure.

Acosta-Cordova said many highways run directly through communities of color. There are also warehouses and distribution centers near highways for easy truck access – and Acosta-Cordova said this placement is critical.

“The people who live around these facilities disproportionately are people of color, African American, Latino and Asian communities,” he said. “We suffer disproportionately from poor air quality, from other health-related issues that are created as a result of that air pollution.”

In the 2020 report, the city acknowledged the impacts of Chicago’s air pollution are magnified disproportionately by structural racism and historic disinvestment in Black and Latino communities.

Last July, the U.S Department of Housing and Urban Development found that Chicago is violating the civil rights of residents by continuing to move polluting businesses from white communities into Black and Latino areas. It demanded that the city revise its zoning, planning and land-use policies in order to stop discriminating against communities of color.

Going forward, Montgomery wants to explore how high resolution mapping can incorporate data associated with healthcare access and health outcomes to quantify burden and inform targeted pollution policy.

“Now we can talk about, you know, where pollution is coming from? But, also, how can we make it better for people? And how do these plans benefit people?” Montgomery said.

Acosta-Cordova said research like Northwestern’s is “really helpful in terms of showing what we’ve been telling the city for years, that this is an issue that’s primarily impacting our communities,” he said.

“We’re in a real public health crisis with respect to diesel pollution, not to mention the impact it’s having on climate change.”

Indira Khera is a Metro Reporter for WBEZ. Follow her on Twitter @KheraIndi