Air pollution: You can bike, but you can’t hide

A recently published study shows bike commuters in Fort Collins, Colorado can reduce exposure to some, but not all, air pollutants by riding their bikes on side streets during commute times.

The science on personal exposure to air pollutants has gone back and forth over the past few decades. Several studies suggest cyclists might reduce exposure to air pollutants by selecting routes far from car traffic. Some studies suggest that cycling to the side of traffic is enough to reduce exposure compared to those inside of cars, because air pollutions drops off (very roughly) with the cube of the distance from the source, while others find the exposure to certain pollutants can still be significant for cyclists riding to the side of the road.

Researchers from Colorado State University in Fort Collins instrumented test subjects and asked them to drive, bike a direct route using heavily trafficked roads (such as they are in Fort Collins), and bike a less direct route using more side streets. They measured exposure to black carbon (BC), carbon monoxide (CO), ultrafine particulates (measured as PNC), and fine particulate matter (measured as PM2.5).

Let’s cut to a map provided by the researchers showing the direct and indirect routes they used in their study. Black shows the main arterials across town, while blue shows collector roads used as alternate routes.

Fort Collins bike route map

This Fort Collins study shows cyclists are exposed to higher levels of pollutants than car occupants. In Fort Collins, the bike commute is slower than the car commute (16 minutes for a 6.3 km driving commute vs 23 minutes for a 6.4 km bike commute, both using the direct route). This longer time on the road translates into doubling exposure to BC, PNC and PM2.5. According to the researchers, “This result suggests that a vehicle offers some protection from particle pollution compared with cycling.”

Biking on side streets does somewhat reduce exposure to BC and CO for the study participants, although PM2.5 and PNC exposure increased to some degree. The alternate route added, on average, only 100 meters and two minutes to the commute, but cyclists reduced cumulative exposure to black carbon and carbon monoxide by 35% and 30%, respectively. Particulate matter exposure went up, however: cumulative PM2.5 was up a modest 3%, while PNC was up 17%.

The fine and ultrafine particles measured as PM2.5 and PNC are a concern because they lodge themselves deep into the lungs, where they enter the bloodstream. This particulate matter is thought to inflame lung tissue; this constant, long-term inflammation in turn leads to asthma and chronic obstructive pulmonary disease (COPD). Some ultrafine combustion products are small enough to be transported from your nasal passages, through olfactory nerves and to the brain, where they damage nerve cells and cause brain damage.

bike fights pollution

The effects of long-term exposure to low levels of carbon monoxide are less understood, but evidence suggests a link between impaired cognitive function for those with this type of exposure to CO.

If you bike, of course, you’re not contributing to the problem, so feel free to be a little smug about that fact that you’re not killing innocent bystanders with your exhaust.

My bike commute is almost entirely along a path away from traffic, though exhaust odors are evident when I pass underneath I-880 and Highway 101, and when I pass through San Jose International Airport.

You can read the full study published in the open Journal of Exposure Science and Environmental Epidemiology: “The Fort Collins Commuter Study: Impact of route type and transport mode on personal exposure to multiple air pollutants.” Via Citylab where several people are engaging an idiot comment troll who insists “If you don’t want to breath it, don’t bike.” Thank you also to Dr John Volkens, Associate Professor of Environmental and Radiological Health Sciences at Colorado State University, for patiently answering my questions about his study.

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