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Why sitting in rush hour traffic is more dangerous than you think

Sitting in your vehicle during rush hour traffic is more dangerous than you think, scientists say as they found alarming results after measuring in-car exposure to pollutants.

The first in-care measurements of exposure to pollutants during rush hour traffic yielded alarming results. Scientists found that the levels of some harmful particulates in the cabins are twice as high as previously surmised.

While most pollution sensors are places on the ground, alongside roads, scientists say that they do not offer precise information about the harmful conditions that drivers are experiencing as exhaust composition changes rapidly.

To explore what drivers are actually exposed to during rush hour, researchers from Duke University, Emory University and the Georgia Institute of Technology strapped specially designed sampling devices into the passenger seats of cars in order to monitor rush hour traffic in downtown Atlanta.

What the devices showed was that there were up to twice as much particulate matter inside the vehicle, compared with the levels shown by the roadside sensors. In particular, in-car pollution contained twice the amount of chemicals that cause oxidative stress, which is thought to be involved in the development of many diseases including respiratory and heart disease, cancer, and some types of neurodegenerative diseases.

“We found that people are likely getting a double whammy of exposure in terms of health during rush-hour commutes,” said Michael Bergin, professor of civil and environmental engineering at Duke. “If these chemicals are as bad for people as many researchers believe, then commuters should seriously be rethinking their driving habits.”

For the experiment, Roby Greenwald, a research assistant professor at Emory at the time, built a sampling device that draws in air at a similar rate to human lungs to provide detectable levels of pollution. The device was then secured to the passenger seats of more than 30 different cars as they completed more than 60 rush hour commutes.

Some drivers took highway routes while others stuck to busy thoroughfares in downtown Atlanta. While other details like speed and having windows rolled down varied, all of the sampling found more risk in air exposure than previous studies conducted with roadside sampling devices.

“There are a lot of reasons an in-car air sample would find higher levels of certain kinds of air pollution,” said Heidi Vreeland, a doctoral student in Bergin’s lab and first author of the paper. “The chemical composition of exhaust changes very quickly, even in the space of just a few feet. And morning sun heats the roadways, which causes an updraft that brings more pollution higher into the air.”

Reactive oxygen species found by this study can cause the body to produce chemicals to deal with the reactive oxygen. Particulate matter causes the same response. In combination, the exposure triggers an overreaction that can be destructive to healthy cells and DNA.

Oxidative stress is thought to play a role in a wide range of diseases including Asperger’s syndrome, ADHD, cancer, Parkinson’s disease, Alzheimer’s disease, atherosclerosis, heart failure and heart attack, sickle cell disease, autism, infection, chronic fatigue syndrome and depression.

“There’s still a lot of debate about what types of pollution are cause for the biggest concern and what makes them so dangerous,” Bergin said. “But the bottom line is that driving during rush hour is even worse than we thought.”

Scientists believe that the high levels registered by their devices are, at least in part, explained by poor city planing.

“My two cents is that this is really an urban planning failure,” said Greenwald, who is now an assistant professor of environmental health at Georgia State University. “In the case of Atlanta, the poor air quality on the highways is due to the fact that 6 million people live in the metro area, and most of them have little choice but to get into an automobile to go to work or school or the store or wherever. Auto-centric transportation plans do not scale well to cities of this size, and this is one more example of how traffic negatively affects your health.”

The results of the Atlanta study were published on June 27 in the journal Atmospheric Environment.

According to the World Health Organization, transport is one of the main sources of air pollution, for which evidence on direct effects on mortality as well as on respiratory and cardiovascular disease is firmly established. About 100 000 premature adult deaths attributable to air pollution occur each year in the WHO European Region alone. Emissions from road traffic account for a significant share of this burden. Some 40 million people in the 115 largest cities in the European Union (EU) are exposed to air exceeding WHO air quality guideline values for at least one pollutant.

Children living near roads with heavy-duty vehicle traffic have twice the risk of respiratory problems as those living near less congested streets.

Sylvia Jacob

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