Cars, trucks and buses emit considerable amounts of airborne pollution as they make their ways along city streets and highways. The fine particles, nitrogen dioxide and volatile organic compounds (VOCs) spewing out of tailpipes have been linked to a wide range of human health problems, from headaches to respiratory illness to cancer. Though Australian researchers found that exposure to these pollutants is actually higher while riding inside a vehicle than while riding a bike, turning your handlebars in the direction of back roads might still be a good idea, for safety’s sake as well.

Western Washington University Geophysicist Bernie Housen, concerned about the air quality on his own bicycle commute along busy Bellingham roads, recently launched a study of the magnetism in local trees to gauge air quality along his route and elsewhere in his region. The magnetism in a tree’s leaves is created by tiny particles of iron oxides and other pollutants that drift through the air, emanating primarily from eroding vehicle brake pads and diesel exhaust. The particles are small enough to pass through our nasal passages and get lodged in our lungs. Housen and his colleagues found 10 times as much magnetism on urban roadside tree leaves as on their rural counterparts that contend with little traffic.

Housen has also altered his own bike route to campus to avoid the more polluted thoroughfares. “One underlying concern is that if you are riding your bike, you are being more physically active; you are breathing deeper and breathing more air in, and so if you are doing that in an area where there is a concentrated elevation of this material it might not be such a good thing,” he added.

Ironically, many cities that offer dedicated bike lanes often lay them out right next to busy bus lanes, unintentionally ensuring that bicyclists breathe in as much diesel exhaust as possible. “I ride along one of these high-traffic bus routes,” Housen says, “and … there was between two and five or six times more magnetic fine particulate matter along the bus route than [on less-busy streets].” Housen would like to expand his research so it could be used by urban planners to better design bike and pedestrian routes so as not to intermingle so much diesel transit and pedestrian/bicycle traffic.

Of course, there are other ways to track urban pollution levels. In the UK, for instance, researchers from the government-funded Engineering and Physical Sciences Research Council have created the Urban Pollution Monitoring Project, which builds and distributes GPS-enabled mobile pollution sensing systems that can be carried by hand or placed on a bike rack. The group is using data gleaned from the sensors to map where and when pollution levels are at their highest around London and other UK cities, and hopes to use its research to influence the way roads and urban areas are planned in the future as well.

Those who want or need to keep on riding through polluted areas should consider wearing an anti-pollution respiratory mask, many of which can filter out upwards of 95 percent of particulate pollution before it enters the human lung. Some leading manufacturers include Totobobo, G-Flow and Respro.