Sonia Monet Saxon often wakes up around 4 a.m. to the smell of burning asphalt.
Her McKinley Park home is close enough to an asphalt plant that the stench makes it difficult to go outside some days.
Long before wildfire smoke from Canada and Minnesota brought record-breaking levels of PM2.5 to the Chicago region a week ago, pollutants have been an ever-present problem in many communities.
That’s why, a day before the smoke plumes descended, Saxon was using zip ties to fasten an air quality sensor to the railing of a house in McKinley Park, the latest of 15 or so installations she’s done over the past few years. Her goal is to monitor pollution from the asphalt plant.
“I love this neighborhood so much, but if you were here yesterday or the day before around this time, it would smell like burning asphalt,” she said. “It was almost unbearable to be outside.”
Air quality in Chicago is measured in different ways, from fairly cheap sensors such as the one Saxon installed to the sensors in the network set up last summer by the city of Chicago and University of Illinois Chicago. Then there are the sophisticated regulatory monitors that are much more expensive and complicated to use.
UIC professor Serap Erdal, who leads the Open Air Chicago project, said it’s the second-largest air monitoring network of its kind in the world behind London.
But even then, the sensors only measure static points spaced throughout the city. In the future, satellites could fill gaps in air monitoring coverage for the city and the many regions of the country where there is no coverage, according to recent studies.
Yet some advocates say better air quality tracking still doesn’t do enough to address the root causes of pollution.
“Our goal is not to know how bad the air we’re breathing is,” said Anthony Moser, board president of Neighbors for Environmental Justice, a community group based on the Southwest Side. “The goal is to breathe clean air.”
Neighborhood air sensors
Saxon, 39, is a community science organizer at the environmental advocacy group. It focuses especially on the MAT Asphalt plant in McKinley Park. Ever since opening in 2018, the plant has faced criticism over its proximity to a school, major public park and homes.
Saxon said she’s installed sensors manufactured by PurpleAir in McKinley Park and other neighborhoods with elevated levels of air pollution. These sensors cost $289 each, according to PurpleAir’s website. Saxon said the monitor she recently installed was purchased with a grant from UIC.
Data from these sensors is available to the public online. The sensors measure a few things, including fine particles known as PM2.5.
PM2.5 can be emitted by factories, power plants, diesel and gasoline vehicles, residential fireplaces and wildfires. The fine particles can harm human health and sometimes be deadly.
The sensor freshly installed by Saxon on July 15 first showed a PM2.5 rating of 58 — then jumped to 71 two minutes later.
Both numbers are within a range PurpleAir lists as acceptable, but the website details potential risks with a full day of exposure, especially for people unusually sensitive to air pollution.
As Cook County filled with record-breaking PM2.5 levels from wildfire smoke on July 16, the sensor read 595. AirNow, a website that combines data from county, state and federal air quality agencies nationwide, reported PM2.5 levels in similar ranges in Chicago that night.
Anything above 300 is considered a “health warning of emergency conditions.” These conditions are hazardous to everyone.
In September, Chicago and UIC finished installing sensors for Open Air Chicago. Solar-powered sensors were placed on light poles across the city.
Industrial neighborhoods with a heavier pollution burden identified by the Chicago Environmental Justice Index received more sensors. Thirteen organizations, one of which was Neighbors for Environmental Justice, helped decide sensor locations. Many of them were placed near daycares, schools and hospitals, according to UIC’s website.
Erdal said findings from Open Air Chicago aren’t ready to be shared yet.
Angela Tovar, the city’s chief sustainability officer, said the city’s sensors are not used to enforce air quality regulations but instead give residents real-time information about the air in their neighborhoods.
“It’s an important tool as we talk about air quality. We want people to understand the data in their community,” Tovar said. “We’ve even used that as a resource as recently as last week during the wildfires, making sure people knew there was a tool that could show, at a very granular level, what air quality looked like in their community.”
She said the network helps city officials identify pollution patterns that could inform future enforcement plans.
“It certainly allows us to see trends and concentrations of air pollution that we should be concerned about,” she said. “That could help inform future strategies for how we approach enforcement across the city.”
Residents who want to check the air quality in their neighborhood can go to the Open Air Chicago map and click on a sensor nearest to their location to find readings on pollutants.
Erdal said a website for Open Air Chicago will launch in the next few weeks with sensor data and educational resources.
“The website not only will serve as a data-dissemination platform, but most importantly, it will also serve as a community education platform,” Erdal said. “We are trying to really make the data to be useful, understandable, to the public.”
Within legal limits
Even though Open Air Chicago is operational, Neighbors for Environmental Justice members still install their own air sensors. That’s for a few reasons. Moser said although the city’s air sensors are “an achievement,” they can still be a mile or more apart, leaving gaps in coverage.
The environmental advocacy organization also started installing sensors before Open Air Chicago put up its own devices and made the data publicly available. Additionally, showing people data on their own streets or homes can help air pollution seem more tangible, Moser said.
“I find (sensors) to be a compelling way to get people to engage with the idea of air pollution as a real thing,” he said. “It’s easy for it to be kind of invisible.”
The relationship between Chicago’s asphalt plants and air pollution is well documented, Moser said, and knowing the levels only does so much.
Zoning and planning laws also make it easier for developers to build in certain neighborhoods, particularly in communities where many residents are low-income and people of color, Moser said.
MAT Asphalt facility manager Joe Haughey said he gets calls regularly from a member of Neighbors for Environmental Justice complaining about odors coming from MAT Asphalt.
“I’ll say, ‘Where are you standing, what intersection? I don’t need to know your home, but I would like to meet you somewhere in the area where you’re smelling this,’” he said. “Not once has that person ever taken me up on that.”
Haughey pointed to testing showing MAT Asphalt was well within legal limits for emissions. According to a 2022 MAT Asphalt news release, CleanAir Engineering, a testing and consulting firm in Palatine, found the plant’s particulate matter emissions to be less than 1% of permitted levels.
Haughey said if parts of McKinley Park have noxious odors, it’s due to sources other than MAT Asphalt.
“I personally believe odors are a chosen complaint because of how arbitrary they are, meaning no one is going to tell somebody that they didn’t smell anything,” Haughey said. “It’s a very hard thing to prove if someone is being disingenuous about what they smell.”
Truck traffic
A lot of air pollution doesn’t come from plants but from industrial corridors in the city and suburbs where large trucks bring materials in and out. Little Village and south suburban Elwood residents are among those who have organized after diesel emissions near their homes were predicted to increase significantly because of warehouse developments.
A state bill requiring emission targets and buffer zones between warehouses and nearby neighborhoods failed to advance in the General Assembly’s spring session.
Baltazar Enriquez, president of the Little Village Community Council, said the group organized a commission focused on improving air quality in the community.
“We’re fighting for our children to have a place to play, and they’re, later down the road, not going to be diagnosed with asthma or lung problems,” he said.
Air monitoring is also on his mind. Enriquez said the community has PurpleAir sensors set up. But these sensors can only detect so much, and he said some haven’t functioned as they should due to the weather or being incorrectly calibrated.
“We want a more efficient air monitor that detects everything,” Enriquez said.
Sensors vs. monitors
Chicago has six federal air monitoring sites, according to the city’s website. These sites contain “regulatory monitors” more sophisticated than the sensors used by the community group and Open Air Chicago.
“It takes, you know, a very well-trained person, a chemist, to operate and interpret these instruments, but they’re both accurate and precise,” said Zac Adelman, executive director of the Lake Michigan Air Directors Consortium.
Regulatory monitors are used to “assess compliance” with federal air quality standards, according to the city of Chicago’s website. Adelman said there’s not many regulatory monitors due to how expensive they are.
That makes the cheaper sensors an attractive option for many. Adelman even has one from PurpleAir attached to his house. However, he said there are limitations to tracking air quality with sensors.
The ability for sensors to accurately measure air pollution is lower, and they’re more vulnerable to environmental conditions such as temperature or humidity changes, Adelman said. Sensors that show up on a public map could be placed anywhere.
“When you look across the PurpleAir map, sometimes you see sensors that are reading, like, anomalously high compared to the other sensors in the map,” Adelman said. “That could be in somebody’s kitchen or on top of their barbecue.”
Satellite tracking
Another issue is there’s just not enough regulatory air monitors to measure the whole country.
“There’s more than 3,000 counties in the U.S., but less than 1,000 of them have any kind of monitoring at all for one of these pollutants,” said Kevin Stewart, director of environmental health for the American Lung Association.
One unmonitored area among Chicago’s collar counties is Lake County, according to data provided by Tracey Holloway, a professor at the University of Wisconsin at Madison. Lake County is one of the roughly 80% of U.S. counties without a regulatory monitor for fine particulate matter, Holloway wrote in an email. Illinois only reports air quality data for 23 of its 102 counties, according to the American Lung Association’s website.
Stewart and Holloway co-authored studies showing satellites as a possible means of filling that gap. Satellites gather data about the sky from above, which is then processed to calculate PM2.5 concentration.
“One of the powerful characteristics of satellite data is that they can see in between the monitors; they can see where there are no monitors; they can see over water bodies,” Holloway said.
Satellite data isn’t a silver bullet, though. Holloway said the process of watching air pollution from above is “harder than it sounds.” She compared it to looking down into a pond and seeing fish. It’s easy to count the fish, but telling how deep in the water they are is much more difficult. Viewing pollution from space is similar, she said.
Adelman said satellite monitoring is useful because it’s able to analyze a continuous area, instead of just one point in space. But there can also be complications depending on the weather and what’s on the Earth’s surface.
“You don’t see what’s happening at night,” Adelman said. “They have issues retrieving over water because of the real reflectivity of the surface.”
Satellite data could ultimately be part of a complex ecosystem of air monitoring in Chicago and the U.S. — one that ranges from government-operated monitoring stations all the way to gadgets installed on front porches.
As the sensor Saxon installed kept reading higher and higher on July 16, air pollution was on residents’ minds citywide. But some people living in McKinley Park think about it every time a certain stench fills the air.
“I’m always trying to find new ways to talk about it, because a lot of these issues haven’t changed,” Moser said. “A lot of these are the same issues we’ve been having, and what needs to change is the city taking this seriously.”
Freelancer Christiana Freitag contributed.
