Louisville has always struggled with air pollution—from industrial parks and from the traffic-clogged highways. But while Metro Government’s network of air monitors tests the air around the city, it’s harder to tell what residents are actually exposed to in their homes.
In the Portland neighborhood, I-64 rumbles past rows of shotgun houses, many with siding made grimy by the traffic exhaust. The highway is loud and dirty, but its pollution isn’t the primary concern for many residents.
“It never occurred to me to think about it all, actually,” says Crystal Glaab. When she and her husband bought their house on Portland Avenue, the pollution from the roadway didn’t factor into their decision. The proximity of the road just represented convenience.
“I just always figured it as a bonus. I mean it’s ugly, but it’s right there, you know?”
Pollution is visible in some places—like when a truck belches out smoke, or dark particles blacken white siding. But it’s harder to see indoors. Which is why last summer, I tested the indoor air quality in 17 homes around Louisville, including Glaab’s.
I was testing for black carbon, and found significant amounts of the pollutant infiltrating inside, despite the fact that the Glaabs keep their doors and windows closed.
There are two main types of air pollution in Louisville: ozone and particle. In the summer, ozone is a problem—it’s usually what sets off air quality alerts. But particle pollution can be an issue year-round—it’s made up of soot, dirt, and other tiny particles.
One of those “other tiny particles” is black carbon. And it comes from a lot of different places, including auto exhaust, wood burning fireplaces and even frying meat.
Black Carbon and Its Risks
“Black carbon is produced anytime you burn something, basically,” said Sarah Doherty, a senior research scientist at the Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington. “And in particular when you burn something inefficiently.”
Like other air pollution, black carbon has been linked to human respiratory and cardiac problems. Recent studies suggest it’s the second-largest contributor to climate change worldwide.
Black carbon is a bigger problem in some places than in others. Large American cities—New York, for example—have high levels, mainly because of traffic. Developing countries—such as Bangladesh—have even higher levels, because of open cook stoves and wood burning.
So what about places like Louisville—neither major metropolitan hubs or developing nations?
As my air monitoring revealed, it’s complicated.
For the testing, I used small monitors that check black carbon every three minutes.
All the tests were on different days, so a higher carbon reading could be unique to the home and neighborhood, or it could just reflect Louisville’s air at that time.
‘It’s Just the Price You Pay for Living Here’
The quick summary of the data wasn’t much of a surprise. The lowest average black carbon concentration was in Prospect, several miles from the interstate. The highest average concentration was about nine times that, at the Glaab’s house in Portland. Click here to see all of the data.
“It’s just the price you pay for living here, I guess,” Geoff Glaab said, once I showed him the data. He’s not surprised that his home had the highest black carbon levels.
“It’s cheap to live here, it’s close to downtown, but it’s also very close to the interstate, so you have to factor that in as well…It’s not like I can move and it be that much better,” he said.
Most of the black carbon in the United States comes from traffic—specifically, from diesel exhaust. Studies have shown that homes in close proximity to major roadways have higher levels of black carbon than those farther away.
But the rest of my data didn’t fit as neatly. A home right off busy Cane Run Road was on the lower end of the spectrum. There were high levels off Poplar Level Road, near the Louisville Zoo, and an unexplained nighttime spike in a monitor placed in off of Brownsboro Road, near the Louisville Country Club.
To make things even more complicated, the Louisville Air Pollution Control District has one air monitor—on Cannons Lane—that separates carbon from the particulate matter it collects, and calculates an average every three days.
This data isn’t necessarily the best indication of individual exposure across the city; because black carbon is very localized—an old diesel truck idling on your street would affect your exposure to black carbon, but wouldn’t necessarily register on a monitor miles away. But in at least a couple of homes—the Glaab’s, and a home off Poplar Level Road—the black carbon levels were much higher than the monitor registered that day.
You can see all the data here in the interactive map accompanying this article. And you’ll find all of the homes—no matter whether the windows were open or closed—registered some amount of black carbon.
Steven Chillrud of Columbia University’s Lamont-Doherty Earth Observatory said it’s likely most of that pollution came from the outside.
“Well, particulate matter actually penetrates fairly well into the home,” he said. “Unless you have centralized air conditioning with a good filtration system on the fresh air that you bring in from outside and really tight windows, particulate matter can penetrate quite well.”
Black carbon can come from inside the house, too. None of the people I tested were smokers, but cigarettes are a common source. Cooking and burning meat generates black carbon. And using an exhaust fan helps keep it from spreading out of the kitchen.
But for the most part, black carbon, like other air pollution, is something harmful you can’t really control. What’s worse, University of Minnesota professor Julian Marshall says there are often lots of insurmountable hurdles for private citizens who want to monitor what’s in their air.
“It varies in space, concentrations vary in time, there’s many different pollutants that I could measure, a lot of the devices are expensive, complicated, and then interpreting those numbers are complicated,” he said. “Those are all challenges. I think all those things you found, that’s just the way it is.”
Funding for this series was made possible through a grant from the Society of Environmental Journalists.