Merritt and her group of volunteer pollution hunters had assumed the low-cost sensors they carried during daily walks would confirm their fast-growing neighborhood had relatively decent air quality, at least when compared with the gritty industrial corridors in other parts of Chicago.
Color-coded graphs that popped up on Merritt's screen during an unseasonably warm October afternoon told a more complicated story. Something as common as a CTA bus or city garbage truck passing by caused the amount of lung-damaging particulate matter in the air to temporarily jump off the charts.
Just as concerning were spikes of pollution that turned up when the group reviewed data from a different air monitor stationed for three weeks in Dearborn Park, a quiet, tree-lined square framed by high-rise condominiums.
The volunteers now are eagerly awaiting a review of their handiwork by scientists who oversaw air monitoring in the South Loop and three other Chicago neighborhoods during the past six months. Funded by the U.S. Environmental Protection Agency, the project is part of a broader nationwide effort to use rapidly developing technology to give people easy-to-access information about pollution they breathe during their daily routines.
"We came into this thinking we would be a control group they could use to compare to other neighborhoods with environmental justice issues," said Merritt, a management consultant who leads the Alliance for a Greener South Loop. "Given all of the vehicle and train traffic around us, it looks like we have our own pollution problems."
Breathing even small amounts of particulate matter, commonly known as soot, can inflame the lungs and trigger asthma attacks. Long-term exposure can cause heart disease, increase the risk of developing cancer and shave years off a person's life.
Unlike the thick clouds of pollution that choked cities during the past century, the soot particles that concern public health researchers today are so small that thousands could fit on the period at the end of this sentence.
Since the amount of vehicle exhaust and factory pollution can vary widely within neighborhoods and at different times of day, the new wave of portable and stationary sensors can find pockets of dirty air that go unnoticed by authorities.
Intrigued by the potential of using personal technology to track the invisible-but-deadly pollution, the EPA began awarding scientific grants during the Obama administration to determine if relatively inexpensive sensors developed by tech startups and hobbyists could supplement a network of official monitors.
Regulators already measure soot at 17 sites in the Chicago area, and other monitors collect snapshots of data on smog, heavy metals and volatile chemicals to assess air quality across the entire region. But the bulky, expensive equipment isn't mobile and the testing is designed to give a glimpse of the entire region, not identify hot spots. The closest soot monitor to the South Loop is more than 5 miles away.
Nobody thinks the new technology is reliable enough yet to be used in court or a regulatory proceeding. Rather, researchers and career staff at the EPA see it as a tool for citizens to conduct their own experiments and draw attention to pollution problems that otherwise might not be addressed, especially as President Donald Trump pushes to dramatically cut funding for federal and state environmental programs.
In addition to Merritt's group, activists from Altgeld Gardens, Little Village and the East Side neighborhood are testing the reliability and ease of use of a half-dozen sensors, including devices small enough to fit on the straps of a backpack, one that looks like a throwback from the original "Star Trek" television series and another the size of a 16-inch softball.
Meanwhile, Serap Erdal, a University of Illinois at Chicago researcher who advises the groups, is testing all the devices next to an EPA monitor in Northbrook to determine how close the readings are to the regulatory gold standard.
Before fanning out again to see if the low-cost devices can endure a Chicago winter, some of the volunteers gathered last month at the nonprofit Delta Institute to share what worked and what went wrong during their summer and fall testing runs.
They reported the instructions and software for some of the devices were too confusing. One had a sensitive power button that would cause users to inadvertently turn off the devices. Another was knocked offline by a spider web.
"Doing good, low-cost sensor work is deceptively challenging," said Scott Fruin, a University of Southern California researcher who studies air pollution but isn't involved in the Chicago project. "Many of the sensors are not up to the task."
Some of the volunteers chafed at filling out paperwork vital to helping their scientific advisers determine if spikes of pollution detected during their testing runs are meaningful or were merely the result of a sensor malfunction. Yet organizers said people of all ages are excited to keep going, driven by the idea they could someday figure out themselves if their suspicions about neighborhood air quality are valid.
Community leaders say the technology also gives them new opportunities to expand their networks and engage with neighbors reluctant to get involved.
"It really seems like we're entering a new renaissance in the environmental movement," said Sammy Corona, a volunteer with the Southeast Environmental Task Force who excitedly told the Delta Institute group about a recent conference that highlighted an elaborate network of air monitors in Southern California.
"When I got back," Corona said, "I realized we are still in the Dark Ages in Chicago."
The neighborhood experiments are just one example of how the nation's third-largest city is catching up.
Researchers at the Urban Center for Computation and Data, an initiative by the University of Chicago and Argonne National Laboratory, have developed equipment that is being posted on light poles around the city to provide granular details about air quality, traffic, sound volume and temperature.
After working out glitches with the electronics and redesigning protective enclosures for the devices, dubbed the Array of Things, the scientists are planning to have 500 monitors up and running by the end of next year.
Charlie Catlett, a data scientist who directs the project, said the goal is to provide researchers and the public with new kinds of data that can be used to improve quality of life. The latest version of the monitors is designed to make it easier to add new technology as the field improves and expands.
Catlett's project echoes a long-running study by the New York City Department of Health. Former Mayor Michael Bloomberg's administration relied on borough-by-borough maps of data from pole-mounted sensors in an effort to stop landlords from using sooty fuel oil to heat apartment buildings and switch to cleaner-burning natural gas.
In 2010, the Tribune used a handheld sensor to test air quality on Metra commuter trains and inside stations that more than a quarter of a million people pass through every weekday. The newspaper found spikes of noxious diesel soot inside passenger cars after the doors closed on outbound trains and locomotive exhaust was sucked into ventilation systems.
Metra responded by installing more effective filters that improved air quality inside the cars. But commuters still routinely complain about hazy clouds of diesel pollution inside Union Station and Ogilvie Transportation Center.
Another early adopter of personal air testing devices is the Environmental Law and Policy Center, a Chicago-based nonprofit that loaned Walkman-size sensors to students, neighborhood groups and others between May and October to measure soot in 35 of the city's 77 community areas.
The testing found high levels of soot along major thoroughfares and at clogged intersections throughout the city. Howard Learner, the group's executive director, said as more data is accumulated, it can nudge city officials and citizens to make changes.
For instance, CTA bus drivers could stop idling at busy transit stations or transportation engineers could tweak traffic signals to reduce backups when pollution hot spots are detected. People could rely on the maps to avoid dirty air while commuting or walking around the city.
"We already have reasonably verifiable data that can be collected by people engaged in their communities, and the equipment is only going to get better," said Learner, who co-chaired an EPA task force that last year urged the agency to boost its support for citizen science. "By identifying problems in ways that weren't possible before, it opens up new opportunities for solutions."
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