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What Walks Through Louisville Reveal About Black Carbon Exposure

In Louisville, a city bisected and ringed by interstate highways and in the midst of expanding its concrete infrastructure, it’s hard to get away from traffic pollution. Every day, cars and trucks belch out cocktails of gases and chemicals, such as arsenic, nitrogen dioxide and fine particles.

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Scientists agree: breathing in large quantities of this pollution isn’t healthy. Steven Chillrud of Columbia University’s Lamont-Doherty Earth Observatory said it’s pretty safe to say that breathing the air near a highway could have health consequences—at least for some people.

“Certainly for susceptible subpopulations like asthmatics and people that are at high risk for cardiovascular disease, breathing in combustion products is not good,” he said.

Still, it’s hard to know what your personal exposure is as you move around the city. So I took two walks, carrying an air monitor with me. The first was designed to be traffic-heavy.

I walked along Arthur Street right by the University of Louisville—basically the closest you can get to I-65 without actually walking on the interstate. It’s really not a pleasant walk. There’s lots of traffic. As I walk under an overpass, a train crosses overhead.

The second walk was further from the highway. I left my house in the Highlands, hit Eastern Parkway and walked along Cherokee Park’s scenic loop, the whole time with an air monitor attached to my hip.

So, what exactly was I breathing during those two walks?

How Particle Pollution can be Harmful

One of the things that makes diesel exhaust harmful to humans is the prevalence of tiny particles that can penetrate your lungs and get into your bloodstream, aggravating diseases and causing inflammation.

But any small particle is considered particle pollution—including dirt and soot. For years, scientists have been pointing to compelling evidence that it’s not just general particle pollution that causes all these health problems, but specifically, particle pollution from cars and trucks.

By studying people who live near major roadways and comparing them to people who live further away, researchers have been able to point to traffic-related particle pollution as a major health concern.

In one study, Tiina Reponen, director of the University of Cincinnati’s Education and Research Center,studied persistent wheezing in two groups of young children—those who lived within 400 meters of a major road and those who lived more than 1500 meters away. Her study found the toddlers with higher traffic exposure had higher instances of wheezing.

“They were almost two times more likely to have wheezing than children who had low traffic exposure,” she said.

Reponen said there was clear correlation between the traffic and health problems. But then her team separated the diesel exhaust particles from the rest of the pollution.

“It seems that diesel particles, and particularly elemental carbon that comes from diesel, seems to be the one that’s pinpointed as the reason for the health effects,” she said.

And that black—or elemental—carbon was what I was testing for during my walk earlier this summer.

Black carbon is created by incomplete combustion—everything from burning meat to wood stoves to fossil fuels. But the biggest source of black carbon in the United States is from diesel engines. And University of Minnesota professor Julian Marshall said it’s emerging as a good way to accurately measure pollution from traffic exhaust.

“There are many different sources of particulate matter, including chemical formation in the atmosphere. And that’s not true for black carbon,” Marshall said.

“There are just fewer sources and there’s not black carbon that forms in the atmosphere. So that’s why black carbon is more of a tracer for combustion than particulate matter would be.”

Besides being a good indicator for traffic, research is starting to indicate that black carbon might be more dangerous to health than particle pollution as a whole. A Dutch study from 2011 found an increase in black carbon concentrations (of one microgram per cubic meter) led to a 7-to-8 time increase in mortality rates, when compared to an identical increase in particulate matter concentrations.

What's in the Air?

I used a device called a MicroAeth, rented from a company in San Francisco. I also gave a monitor to my neighbor, Craig Lee, who set out on a different day to bike a portion of the Louisville Loop.

All of these tests were done on different days, at slightly different times. This means they can’t really be compared because weather conditions were different, and the black carbon concentrations in the city varied, too. But I was surprised by the results.

  • Lee was exposed to an average of 1.2 micrograms of black carbon per cubic meter during his bike ride. The highest levels—about 6 micrograms per cubic meter—came when he was riding back to his home along Broadway.

Louisville Loop

  • During my walk near I-65 and the U of L, I was exposed to an average of 1.1 micrograms of black carbon per cubic meter. The highest levels were 5.7 micrograms per cubic meter, around where East Burnett Avenue intersects with the I-65.

Highway Walk

  • And during the walk to and around Cherokee Park, I was exposed to an average of 1.5 micrograms of black carbon per cubic meter. The highest recorded level during the walk was a whopping 17.3 micrograms per cubic meter, which came near the intersection of Bardstown Road and Eastern Parkway.

Cherokee Park Walk

According to the monitor, I was exposed to 75 percent more black carbon during the bucolic Cherokee Park walk than the walk near the highway.

This could be a fluke, or it could be because I got held up at a busy intersection, where I was in close proximity to idling cars. Both of the walks showed black carbon levels within the average background range for major American cities (which is 1-3 micrograms per cubic meter).

But no level of exposure to black carbon is necessarily safe. The federal Environmental Protection Agency issues guidelines for particle pollution—the annual average can’t exceed 12 micrograms per cubic meter, and the daily average can’t exceed 35 micrograms per cubic meter—but there aren’t current regulations on the concentration of black carbon in the air.

Cleaner Air Through Technology

The federal governments and some states have taken steps in recent years to reduce diesel emissions in particular.

Federal regulationshave required all newer trucks (model year 2007 and after) to use ultra-low sulfur diesel and be equipped with newer pollution controls. Trucks built after 2010 have to meet even stricter regulations, and the EPA estimates the rule will reduce particulate matter by 110,000 tons a year.

And there are efforts happening on the local level, too. Since 2008, the EPA has given out millions of dollars in grants to cities and states across the country to switch from older to newer—and cleaner—diesel technologies. Louisville Metro Government got some of that money last year, when it used more than $1.6 million in federal and state grants to retrofit 90 pieces of city equipment.

Louisville’s TARC buses are slowly being replaced with cleaner and hybrid models, but a spokesman said about 60 percent of the city’s fleet is pre-2007.

“We’ve done a lot to try and clean things up. We’ve got the particle traps on diesels now, we’ve got much cleaner burning fuels, we’ve got much cleaner burning engine designs in our vehicles,” said Philip Hopke, the director of the Center for Air Resources Engineering and Science at Clarkson University.

And while diesel emissions are the major source of black carbon in the United States, open fires and cook stoves in developing nations are also a concern. They cause millions of premature deaths around the world, primarily of women and children.

But black carbon’s health effects are only half of the picture. Recently, researchers have been connecting black carbon to climate change. They say the particle plays a much larger role than previously thought.

“We need to look at it both from a health and a climate perspective," Hopke said. "Whatever works to develop the will to make things happen."

Go here to read other stories in this series on black carbon.

This series will continue tomorrow.

Funding for this series was made possible through a grant from the Society of Environmental Journalists.

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