For millions of Americans, the rush-hour commute is more than just frustrating. It’s also dangerous, exposing drivers to unsafe levels of air pollution. Rolling up the windows won’t solve the problem. An ongoing study in Atlanta has found that people are exposed to more pollution sitting in the driver’s seat than they would be watching traffic on the side of the road. Roby Greenwald, an environmental scientists at Georgia State and part of the study’s research team, spoke with Nexus Media about the dangers of rush-hour pollution — and what we can do about it. This interview has been edited for length and clarity
Is it surprising that rush-hour drivers are exposed to a lot of pollution?
It wasn’t counter-intuitive, but the thing that raised our eyebrows the most was how different pollution levels were inside the car when compared to next to the roadway. We’re only talking about a distance of say 50 feet, but it was twice as high when you’re right there in the car, and that was a very consistent finding. The most important factor is how many cars are around you.
Everyone who volunteered to participate in the study used their own car — 60 different cars, all makes and models, some diesel and some hybrid. We measured things like black carbon inside the car — basically soot coming form the diesel vehicles — the PM 2.5 values [a measure of tiny, hazardous particulate matter], and the number of particles.
We’re measuring the sound they’re hearing in the vehicle, and we’re collecting particles on filters so we can measure the chemicals present on those particles inside the vehicle. We would get measurements every minute, or every second in some cases.
Where did the pollution come from?
You can tell the difference between a particle that came from a brake pad and a particle that came out of a tail pipe. We can also tell that there are particles already in the air… particles that came from burning coal to produce electricity 100 miles away — we can still detect those inside the car.
We can also see particles that come from the vegetation that’s nearby and dust on the side of the road, things like that. The high level of particles inside the car is probably related to the fact that, in the middle of the freeway, you’re right in the plume of the emissions from all the other cars around you.
How is pollution in the car affecting our health?
When the particles deposit in your body, where they go depends on how big they are. A lot of health effects are related to the really small particles, which are able to go all the way into your alveoli, down into the deepest part of your lungs. Once they get deposited there, they’re exposed to the surface liquid that’s on the epithelium of your airways and your alveoli, and they can start to cause oxidation reactions.
You’re exposed to oxidants naturally, so your body’s pumping antioxidants out to try to neutralize these things. The hypothesis is that adding this extra dose of oxidants overwhelms your body’s ability to neutralize them, so then you start seeing the effect of oxidation reactions taking place. Your cell membranes are made out of lipids, so you’ll see lipids start getting oxidized and shed, and you can measure that in your breath.
If that process keeps continuing, then it starts contributing to an inflammatory process, and you start to get inflammatory cells being recruited into the lungs. That initiates a cascade of events that you might not necessarily notice. Susceptible people might actually notice. They might feel bad. They might feel irritation in their lungs. But, it’s contributing to increased systemic inflammation that happens repeatedly, every day, over the course of years.
Through epidemiology, we start seeing the effects of chronic exposure to this kind of pollution, which increases mortality from cardiovascular disease, things like that. The hypothesis is that oxidant-generating reactions occurring after these particles deposit are the initiating step that starts the ball rolling down the hill.
The take-home message is that it’s OK to keep your windows rolled up? It’s cleaner?
We weren’t really trying to measure this. It wasn’t really a goal of the study, but one of the things we did notice was that people who had newer cars, they did tend to do a better job of keeping the outside air from coming in.
In a BMW that was almost brand new, you really could see a difference when they had their windows rolled up. But even so, even in the best of the cars that we had in our study, you still saw huge increases in pollution concentration when some really dirty truck went by you — even with a really good filtration system and seals.
Think about all the spots in the envelope of a car where you have some kind of transition between two materials. That seal has little micro holes in it, it’ll start to age over time, get a little more leaky. You’ve got all these doors that people open and shut all the time. So you have all these little avenues for things to sneak in. And then you’re pushing that thing through the air at 60 miles an hour, and you’re ramming it through the air pretty fast, and stuff can really work its way in.
So what does this say about urban design?
We weren’t really trying to measure the impact of urban designs. But, what’s very, very clear is that these exposures are related to how many cars are around you. When you’re talking about a city like Atlanta, which is kind of famous for being car-dependent for most of the metro area, you have all of these people who are on the roads at the same time.
They don’t really have any choice, and you can’t build roadways big enough to swallow them all, so you have all of these cars squeezed into this space, and you’re being exposed to the emissions from hundreds of cars around you while you’re traveling on these conduits. That model is basically optimizing your exposure to the pollution.
It’s an urban planning product; you’re putting all of these cars in the same spot. If it weren’t necessary for you to be in a car to go somewhere, then you wouldn’t have that problem, or if you were in a smaller city that didn’t have this many cars, it wouldn’t be as big of a problem.