Years ago, we were warned not to jog next to heavily trafficked streets, since that would cause us to inhale a lot of dangerous fumes. We assumed that walking or riding a bicycle in an area filled with cars would cause people to inhale more pollution than they would if they were riding in one of the cars (or in a taxi or bus), but it turns out the OPPOSITE is true.

Bjorn Carey writes in that vehicle passengers inhale much more pollution than pedestrians, whether the pedestrians are walking, running or riding a bike?despite the deep breathing that strenuous exercise demands. In this case, “pollution” refers to ultrafine particles in the air which are so small that large amounts can be inhaled in a single breath. They settle in the lungs and damage cells. These particles are the most serious result of air pollution.

Researchers measured the levels of ultrafine pollution particles from the tail pipes of vehicles on busy city streets and found they mostly affected the people INSIDE the vehicles. Taxi riders were exposed to more than 100,000 ultrafine particles per cubic centimeter. Bus riders were exposed to around 100,000 and people in cars to about 40,000, while pedestrians and bicyclists were exposed to only 5,000 to 8,000.

How can this be? It’s because people sitting in a car in the middle of heavy traffic are directly in the path of the main source of the pollution, which is the muffler of the car in front of them. Biker riders stay mostly on the outer edges of the street, where pollution levels are low, and pedestrians on the sidewalk are even farther away.

Catalytic converters, which are mandatory in the US, remove certain noxious gases from car exhaust, but they do not remove ultrafine particles. In order to protect yourself, the researchers recommend walking close to the buildings, as far away from traffic as possible.

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