When Paula Brooks stands in front of her two-bedroom house on Camp Street in Indianapolis and glances south, she sees brightly painted historic homes and towering oaks. When she glances north, she sees traffic. All day, cars, ambulances, buses, delivery trucks, dump trucks, and semi-tractor trailers rumble by. At rush hour, the traffic crawls as commuters squeeze onto nearby Interstate 65.
"The majority of those heavy vehicles are using diesel, so when it gets congested, you know cars idling, then it really hits you, the fumes," says Brooks, who grew up in this historic African American neighborhood known as Ransom Place.
Those diesel engines spew microscopic bits of pollution called fine particulate matter, which are 30 times smaller than the width of a human hair, roughly 2.5 microns in diameter. (Scientists call this pollution PM2.5) Researchers have linked the particles, which can lodge deep in the lungs and enter the bloodstream, to cardiovascular disease, diabetes, autism, asthma, chronic obstructive pulmonary disease, and even Alzheimer's disease.
In theory, a network of Environmental Protection Agency monitors should help track this pollution in Brooks' neighborhood — and similar places across the country. The most common EPA monitors consist of a metal box with a protruding device at the top to draw in air. Inside are instruments that carefully control the volume of air flow and deliver it to a filtration system that captures pollution particles. Under the Clean Air Act, state regulators are required to put these monitors around geographical regions — usually counties. The regulators then use the monitors' data to show they are complying with the National Ambient Air Quality Standards, which limits how much of a certain pollutant is allowed in a cubic meter of air.
In practice, many experts and advocates say, that system is broken. Data collected by researchers at the nonprofit Resources for the Future, along with studies from at least one academic group, suggests that actual levels of some air pollutants in Ransom Place and other U.S. neighborhoods are higher than what the monitors indicate. There are simply too few monitors, they say, to give an accurate picture of local pollution levels.
Indeed, in Marion County, where Indianapolis is located, there are five PM2.5 monitors to cover 400-square miles. None are in the urban core, where traffic is among the heaviest. "Our stationary monitors are not well suited to pick up our worst emitters," says Gabe Filippelli, a biogeochemist at Indiana University-Purdue University Indianapolis who studies air pollution.
Some researchers suggest that state regulators may have an incentive to keep the limited supply of monitors away from pollution hotspots. And gaming the regulatory system may not be limited to monitor placement. Some recent work suggests that regulators take advantage of intermittent monitoring, an EPA practice that allows regulators to turn on monitors just once every three or six days. Other research shows how facilities may exploit a Clean Air Act provision to avoid penalization by claiming any excess emissions — above what their EPA permit allows — were unintended.
The result of all this overlooked pollution, the researchers say, is that people get hurt — mostly people of color. A 2021 study in Science Advances shows racial-ethnic minorities in the United States are disproportionately exposed to higher levels of PM2.5. The authors modeled pollution concentrations from vehicles, construction, industry, and more, and found Black, Asian, and Hispanic people breathe dirtier air than White people.
This unequal exposure is due to racism, says Julian Marshall, study coauthor and a civil and environmental engineer at the University of Washington. He points to historic discriminatory housing and land-use policies, including mortgage red-lining, which made it so Black Americans and other people of color could not get government-backed home loans where they lived. City planners viewed these redlined neighborhoods as good places for industry and highways because redlining rendered the land cheaper; residents also lacked the political clout to fight such developments. These explicitly racist policies from decades ago still impact the people who breathe the dirtiest air today, says Marshall: "The past is still present."
Traffic near the historic Walker Building at the intersection of Indiana Avenue and Doctor M.L.K. Jr. Street. I-65 traverses the city just to the north. "The majority of those heavy vehicles are using diesel, so when it gets congested, you know cars idling, then it really hits you, the fumes," says Brooks.
For years, the EPA's ground monitors were the only way to measure pollution. Then in 1999, NASA launched a rocket from California's Vandenberg Air Force Base — and with it, a new system for gathering pollution data. Hitching a ride on that rocket was a satellite that flies over every inch of the planet once per day. Along with another satellite launched in 2002, it gathers data on the concentration of pollution particles by comparing solar radiation at the top of Earth's atmosphere with how much is reflected back from Earth's surface — the more particles, the less radiation is reflected back.
Researchers have now been analyzing satellite data for two decades to get a more complete picture of Earth's pollution, but they are still refining the statistical tools needed to interpret the data. Because satellite measurements are not direct samplings of pollution particles, researchers must use a statistical conversion process that at least one study showed can involve a lot of error. This means the data should be viewed with some caution, according to University of California, Berkeley professor Meredith Fowlie, a co-author on the study. In an email to Undark, she explained that the EPA monitors provide a direct measure of pollution; whereas, the satellite-based estimates are "informed guesses coming out of a very challenging prediction exercise."
Still, Fowlie and others see value in looking at satellite pollution estimates to fill in the data gaps inherent among the nation's ground monitoring network. The satellite estimates reveal, for instance, that the monitors may be missing pollution. And some researchers, including Alan Krupnick, a senior fellow at Resources for the Future, and Corbett Grainger, an environmental economist at the University of Wisconsin-Madison, say that may be strategic. Both have been comparing satellite data with ground monitor data and have found evidence that in some counties, including where Brooks lives, monitors may sit just outside pollution hotspots — perhaps because state regulators want to avoid costly investments necessary to bring down pollution levels
EPA officials disagree, pointing to guidelines on where their monitors should be sited. And Barry Sneed, a spokesperson for the Indiana Department of Environmental Management, told Undark via email that his agency follows those guidelines as best they can, adding that "there are limitations to locations that may otherwise be ideal such as vegetation, structures, or the lack of access to power."
In other parts of the country, regulators may be taking advantage of possibly unintended air monitoring loopholes, such as an EPA policy that allows regulators to monitor pollution on an intermittent basis. (EPA data show that the annual cost to operate a monitor that is turned on every day is about $41,000; whereas, to turn it on once every six days is about $21,000.) The one-in-six-day schedule ensures that the monitor will be actively measuring pollution on different days of the week; the EPA says the pollution captured should then average out to a representative number.
But according to recent research by Eric Zou, an economist at the University of Oregon, local regulators may have found a way to skirt this rule. Zou says local regulators are tasked with gathering data to forecast local pollution levels and thus know ahead of time when upcoming air quality may be bad. They also know the day that intermittent monitors will be turned on (the EPA publishes a public schedule). And, critics say, local regulators should know that if they issue a pollution advisory — a warning to residents to stay indoors and drive less — they may be able to quickly lower pollution.
Zou compared daily NASA satellite PM2.5 data to one-in-six-days measurements from ground monitors in hundreds of counties. He found that pollution levels dropped on the day the monitors were turned on, then rose again once they were turned off. He also found that local regulators were 10 percent more likely to issue an advisory, which have names like "Spare the Air," on the days the monitors were turned on. "If you look at when these warnings are issued, look at the timing," Zou says. "You can see a pile up of these issuances exactly on the days when the federal monitors are monitoring."
The Ransom Place Pocket Park gives visitors a window into the history of this historically Black neighborhood. In the U.S., racial-ethnic minorities are disproportionately exposed to higher levels of PM2.5.
A historic home in the Ransom Place neighborhood. Because of where Indianapolis' monitors sit, the state may not be accurately measuring the neighborhood's air quality.
Paula Brooks' mother, Violet, is commemorated with a brick in her name alongside other long-time residents of the neighborhood at the Ransom Place Pocket Park.
Intermittent monitoring can be a problem for other reasons, as residents in Grays Ferry, a formerly redlined south Philadelphia neighborhood, learned in 2019.
On June 21 of that year, three explosions ignited a massive fire at an oil refinery in Grays Ferry. Due to an intermittent monitoring schedule, the nearest hazardous chemical air monitor was off, and other monitors that measure PM2.5 and run on a daily schedule were too far away. With limited data, city officials said the blasts posed no immediate danger to residents. Peter DeCarlo, an environmental engineer at Johns Hopkins University, calls the response "mind-boggling." DeCarlo, then at Drexel University, about two miles north of Grays Ferry, says residents could see a huge black plume of smoke hanging in the air and some told news reporters they could smell burning petrochemicals. "You know, your nose might not spit out a number," he says, "but it certainly alerts you to the presence of things that shouldn't be there."
The refinery's emissions were far beyond EPA limits. Still, the EPA doesn't penalize companies for such accidental emissions, providing they take steps to show it was due to a malfunction, according to Britney McCoy, an environmental engineer who now works for the EPA but was not speaking for the agency in an official capacity. "We know that the refining process is a very complex process in nature," she says, "and so there may be occasions for accidents."
But that accidental emission rule is also ripe for exploitation, according to research McCoy performed before she joined the EPA. In 2010, when McCoy was a doctoral student at Carnegie Mellon University, she analyzed when such accidental emissions occurred at Texas oil refineries and found that they weren't random. "Overall, across all of the refineries in Texas, you see a lot of patterns," she says, pointing out that many happened at the beginning of the week, during morning hours, and during the summer months.
She also found that in communities with several refineries, such as Port Arthur, Texas, these extra emissions created so much pollution that it was equivalent to having another small local refinery.
The findings don't surprise John Beard Jr., who founded and runs the environmental nonprofit Port Arthur Community Action Network. Beard grew up in predominately African American West Port Arthur.
"I was born and raised in this part of town where you have a nice white house and you're sitting out on the porch drinking coffee in the evening, talking with your neighbor and working the flower gardens and the flower beds," he says. "You come out the next day and the side of your house facing the refinery's yellow. Something got released that night. You may have not smelled it because you were asleep." Beard's parents taught him not to turn up his nose at those sulfury smells because the refinery meant jobs. Today he feels differently: "You shouldn't have to sacrifice your health and your environment and where you live in order to make a living."
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While Beard's family chose to live close to the refinery for work, in Indianapolis, Brooks' family had settled in Ransom Place before the highway was built. In 1966, when Brooks was starting grammar school, Indiana state highway officials decided to create a freeway around the city's downtown. It included I-65, which those same officials decided would slice through the city's northwest side, a predominantly African American area. To make room for the steel-and-concrete behemoth, the officials evicted thousands from their homes.
At the time, Brooks lived with her mother, Violet, a few blocks from her present address. The two narrowly missed having to relocate; entrance and exit ramps to I-65 were built just a block away.
Back then, few people considered the highway's impact on air quality. Today, hundreds of studies illustrate the health effects of traffic pollution; a number show that living near a highway — especially within three to five blocks — can lead to impaired lung function, premature death, and fatal cardiovascular diseases.
Despite mounting evidence of harm, nobody is rushing to improve the standards. But even if the EPA did lower the PM2.5 standard, it's not clear how much that would help Brooks. Because of where Indianapolis's monitors sit, the state may not be accurately measuring the quality of the air that Brooks and neighbors breathe. For Brooks, that's not a surprise. She has spent her life witnessing governmental indifference to the fate of Indianapolis's Black residents.
"What fuels my anger more than anything is the destruction of the entire area as a community," she says. "And the health impacts and the lack of greenery that went along with it."
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Nancy Averett is an independent journalist who covers science and environmental issues from Cincinnati, Ohio. Her work has appeared in Discover, Audubon, Sierra, Yale Environment 360, TakePart, Environmental Health Perspectives, Pacific Standard, and many other outlets.
All photos by Faith Blackwell for Undark.