Environment & Science

Freeway commuters breathe dirtier air than previously thought

Traffic jams up trying to enter the 110 freeway, May 7, 2001, in downtown Los Angeles. A new study finds air pollution on freeways is unhealthier during morning rush hour.
Traffic jams up trying to enter the 110 freeway, May 7, 2001, in downtown Los Angeles. A new study finds air pollution on freeways is unhealthier during morning rush hour.
David McNew/Getty Images

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Rush hour just got a lot worse. A new study finds that freeway pollution is twice as toxic than air just off the roadway. And air during the morning commute is worse than during the drive home.

To figure out what commuters are inhaling, researchers at Duke University and Georgia Tech outfitted 60 cars with air quality monitors and sent drivers out on Atlanta freeways and side roads during morning rush hour. They told the drivers to roll their windows up and down every 15 minutes, and to set their cars’ ventilation system to bring in fresh air from the outside, not recycle the air. 

Then, the researchers examined the mix of particles sucked into the cars through their intake systems or open windows. The pollution found included unburnt gasoline, diesel soot and tiny specks of metals that come off brake pads. Not all the particles are equally as bad, but the researchers discovered that the types of particles inhaled by drivers on the freeway during morning rush hour were the more harmful kind.

Breathing the particles they found is twice as likely to cause reactions in our airways that can cause chronic inflammation and may lead to higher risk of asthma, heart disease, even dementia and diabetes.

Study co-author Rodney Weber, an atmospheric chemist at Georgia Tech, said there is just more particulate pollution, period, on the freeway than off.

“When you’re sitting in traffic, the actual concentrations are higher because they haven’t been diluted from spreading out,” he said. “It’s like smoking a cigarette versus being in a room with secondhand smoke. When you’re right close to a source, the concentrations are stronger.”

Time of day mattered, too. In the morning, pollution concentrations in Atlanta are up to 30 percent higher than during afternoon rush hour, the study found, because the air is still and temperatures are lower (this is likely the case in LA, too). That means pollution has not yet dispersed throughout the atmosphere.

The study adds to a growing body of scientific literature showing that sitting in the car on the freeway is bad for us.

A 1999 study by the South Coast Air Quality Management District, one of the first of its kind, found that levels of certain air pollutants were up to 10 times higher inside vehicles than at outside monitoring stations (this ratio has likely come down as cars have gotten cleaner). Freeway air pollution in Los Angeles was especially bad – two to four times worse than in Sacramento. 

In Southern California, commuters living in the Inland Empire are likely exposed to the most air pollution because they are downwind of so many sources, said Scott Fruin, a professor of preventative medicine at USC Keck School of Medicine. They are hit with the same morning rush hour pollution experienced by all commuters, but then they feel the worst effects of smog because sea breezes push pollution east into Riverside and San Bernardino counties during the afternoon.

“That would be quite high exposures compared to the rest of the country, and the rest of LA,” Fruin said.

But there are things drivers can do to reduce their exposure. Rolling up the windows and recirculating the air can cut the concentration of particle pollution inside the car by half to three-quarters, Fruin found in a previous study. Newer cars are better, because they are more tightly sealed, which minimizes the amount of outside air that can seep in. Replacing your air filter regularly is also a good idea. And, of course, avoiding freeways during rush hour, or taking public transit is best.

“The less time you spend in your vehicle, the less this problem applies,” Fruin said. “If you can change where you live or your job, living closer to work really adds up over time – and saves you a lot of time and wear and tear on your car.”