In 2023, O’Hare International Airport and its screaming jet engines were Chicago’s biggest single source of carbon dioxide, accounting for one-tenth of the city’s total.

Half of Chicago’s CO2 came from a transportation system choked with cross-country freight and the worst traffic congestion in the United States.

Only an eighth of the city’s CO2 came from industry, and almost none from generating electricity.

These are highlights from a first-of-its-kind computer model from Crosswalk Labs. The Washington, D.C., firm tracks and visualizes emissions data from every sector of the economy in neighborhoods across the United States.

According to Crosswalk Labs, Chicago’s transportation emissions have been rising since the COVID-19 pandemic, contributing to the city’s total emissions remaining flat despite a promise of steep cuts from a parade of corporate and government leaders.

Americans love to move around. That’s a big reason they’re sticking with carbon-saturated lifestyles despite record heat and raging wildfires worldwide, said Zac Adelman, executive director of the Lake Michigan Air Directors Consortium, or LADCO.

Last month, the National Oceanic and Atmospheric Administration declared 2024 the hottest year on record worldwide and in Chicago.

“It’s bleak,” said Adelman, whose consortium coordinates air quality research for Illinois, Indiana, Wisconsin, Minnesota, Michigan and Ohio.

“Not everyone is an environmentalist,” he said. “And for those people who do care, they’re not sure which actions would be most helpful.”

Crosswalk compiles its pollution estimates by scrubbing every conceivable data source for the number, location and potency of CO2 emitters.

For example, using Federal Aviation Administration data, the company counts every plane that takes off and lands in the United States. It assigns a CO2 value to each one based on its type.

The company uses real-time GPS traffic data from commercial vendors to count cars and trucks.Crosswalk uses annual CO2 reports filed with the EPA for big stationary polluters such as factories and power plants.

Jason Burnett, the company’s chief executive, says neighborhood-level data is more critical than ever as President Donald Trump attacks federal programs. “State, local and private sector leaders are making decisions today that will determine the outcome for climate change over the next decade,’’ Burnett said.

After boiling its data down into census tracts, Crosswalk can build it back up in any number of ways, including by city, county and metropolitan statistical area. It can compare towns and counties on opposite ends of the country.

The Chicago Metropolitan Statistical Area includes 13 counties in northeast Illinois and adjacent parts of Indiana.

In Crosswalk’s list of Top 25 carbon dioxide polluters in Chicago’s metropolitan area, northwest Indiana’s steel mills and oil refineries stand out as battered and lonely survivors after half a century of deindustrialization.

Two steel mills along Lake Michigan emitted more CO2 combined in 2023 than the entire city of Chicago, according to U.S. Environmental Protection Agency data cited by Crosswalk.

Both mills, one in East Chicago owned by Cleveland-Cliffs and one in Gary owned by U.S. Steel, make steel for car and truck bodies.

According to Hilary Lewis, a steel researcher for Washington, D.C., think tank Industrious Labs, the Gary mill alone provides about a quarter of all steel made in the United States.

The East Chicago and Gary mills are also major sources of PM2.5, or small particle air pollution, which damages hearts and lungs. In the 3-mile area surrounding the Gary mill, 97% of residents are people of color, and 62% are low-income, Lewis said.

In addition, according to Crosswalk, a BP oil refinery next door in Whiting emits one-third as much CO2 as the entire city of Chicago.

The refinery converts thick, carbon-rich tar sands crude from Canada into enough gasoline and diesel fuel for 7 million cars daily, plus jet fuel for O’Hare and Midway airports and 7% of all the asphalt used in the United States.

U.S. Steel and BP said they are consistently looking for ways to cut CO2 emissions. Cleveland-Cliffs did not respond to requests for comment.

The CO2 coming from these factories is elusive. Unlike many of the region’s other toxins, people can’t see, smell, taste or feel it, as it lingers in the atmosphere for hundreds of years.

A CO2 molecule from Whiting is no more dangerous to somebody who lives in Whiting than a molecule from Shanghai. But together, all the CO2 molecules everywhere are lifting temperatures across the globe.

Besides being the hottest year, 2024 was also when scientists say CO2 accumulated in the atmosphere at the fastest pace in recorded history, according to a BBC report.

Carolyn Marsh began battling BP pollution when she moved to Whiting in 1987 and saw that the refinery was damaging habitats for migrating birds.

A laid-off steelworker, she’s been helping run a Facebook page called BP & Whiting Watch.

Since August, Marsh has been posting daily PM2.5 readings from an air quality monitor on her front porch.

She also posted an incident report that BP filed with the EPA’s National Response Center on a Dec. 26 chemical spill. The report showed that at least 10 pounds of the carcinogen benzene had been released into the air.

Marsh said the company still hasn’t explained why the chemicals involved in the spill smelled so bad that people were complaining 20 miles away on the north side of Chicago.

BP Spokesman Cesar Rodriguez acknowledged the bad smell near the refinery but said BP didn’t release enough contaminants to threaten public health.

Marsh said she doesn’t know much about CO2 besides that it contributes to global warming, and she doesn’t track it on her air monitor. But she includes it among the long list of pollutants that she says BP routinely downplays.

“We’re a dead zone with miles of pipelines and industrial pollution,” she said. “The air here is thick. It’s not normal air.

“And where’s the local mitigation? We should have free indoor air filters, electric school buses, and 1,000 more trees. This can be done right now, today, tomorrow.”

Joliet and its suburbs are another CO2 hot spot, according to Crosswalk, with half a dozen big petrochemical plants, and six power plants that burn natural gas. The city also has two nuclear power plants within a 20-mile radius.

Industries were drawn to Joliet first by its rivers, railroads and nearby coal mines and then by a dense concentration of oil and natural gas pipelines connected to Texas and Alberta. And some of them are huge.

In Morris, the natural gas-fired CPV Three Rivers Energy Center generates as much electricity as one of the reactors in a nearby nuclear power plant.

Morris, with just 15,000 people, generates more electricity than all but six cities in the United States, according to GridInfo, an Austin, Texas-based data provider on power plants.

Joliet is also an intermodal rail and truck mecca. But the big Union Pacific and BNSF intermodal terminals that attract millions of trucks don’t show up in EPA records as a single stationary pollution source, like a steel mill. So Crosswalk has lumped them together in a broad and amorphous category called transportation, including O’Hare and Midway airports.

According to Crosswalk, residential and commercial buildings account for 38% of Chicago’s CO2 emissions.

Transportation accounts for half. That amount will be hard to cut if, as the Illinois Department of Transportation predicts, the amount of freight moving through Cook County doubles by 2050.

That’s an example of why nearly everyone involved in CO2 polluting is falling short of their goal to improve.

Three years ago, for instance, the city of Chicago set a goal of cutting CO2 emissions by two-thirds by 2040. Since then, the city’s emissions have been flat, according to Crosswalk.

The city measures its CO2 progress in three-year increments, said a spokeswoman for the Chicago Department of Environment. The last review was in 2022, which showed a reduction from 2019, she said. The next CO2 review is expected to get underway soon.

Four years ago, U.S. Steel set a goal for net-zero CO2 emissions by 2050. The Gary mill, the company’s largest, emitted more CO2 in 2023 than when the company set this goal, not less, according to EPA data.

To make faster progress, the company said it hopes to begin capturing Gary’s CO2 emissions sometime next year and converting them into calcium carbonate, a mineral that can be recycled into paper and plastics.

In the meantime, the Sierra Club fought Nippon Steel’s proposed purchase of the company, contending the planet’s atmosphere can’t handle a planned $300 million investment to prolong coal-fired iron-making in Gary for another 20 years.

Five years ago, BP announced a plan to achieve net-zero CO2 emissions by 2050. In 2023, the Whiting refinery, the company’s largest, also emitted more CO2 than when BP set the goal.

In November BP signed a planning agreement with the U.S. government to power a portion of the refinery with hydrogen made from natural gas and then capture and bury the CO2 emitted during the process.

As these reforms crawl forward, Tina Strasny is still trying to live her life in the shadow of the refinery.

At age 60, she’s a costume designer and stitcher for local theatrical companies. She lives in Whiting, 2 ½ blocks from the BP entrance.

Strasny grew up in Whiting and moved back a decade ago after 27 years in Chicago.

Her grandparents were emigres from Eastern Europe and Sweden. Her father and all her uncles worked at BP, and one of her uncles died there in a fire.

They stayed because of what to them was spectacular pay and benefits and freedom from endless political turmoil in Europe. They didn’t think much about pollution, Strasny said, at least not until their later years, when they became boaters, bird-watchers and duck hunters.

Today, Strasny likes looking out on Lake Michigan from her back window.

“There are certain times of the day when you expect certain smells. But it’s not stinky here all the time,” she said. “It’s a very pleasant and safe place. We have a beautiful lakefront park, a beautiful beach.”

An exception, of course, came during BP’s benzene spill the day after Christmas. It smelled like sulfur, tar and acrid, heavy metals all rolled into one, Strasny said, and it was overpowering. For two days she couldn’t sleep.

“I don’t feel like I was struggling to breathe,” she said. “But it was exhausting. It felt like work,” Strasny said.

“Having lived here, I feel like we’re like pigeons who kind of adapt. I can’t prove it’s not affecting me, but I just don’t know.”

Strasny gets annoyed, she said, when Chicagoans criticize “all the dumb people in northwestern Indiana” who’ve failed to stop chemical spills and billowing clouds of CO2 on their own.

“Chicago has to be involved in reducing their usage of the kind of steel and oil we produce here now in northwest Indiana. But Chicago isn’t willing to do that,” she said. “It’s like, everybody who cares about the environment wants someone else to change.”

John Lippert is a freelancer.