Cycling the less polluted routes

Sometimes a detour of less than one kilometre can reduce cyclists’ exposure to atmospheric pollution by 10%! Marianne Hatzopoulou, a professor in the Department of Civil Engineering at McGill University, found that a number of popular cycling paths in Montréal and Toronto are more or less polluted depending on wind direction and traffic volume.

A number of popular cycling paths in Montréal and Toronto are more or less polluted depending on wind direction and traffic volume.

Furthermore, local wind circulation often “purifies” one side of the street within “urban canyons” (streets with tall buildings down both sides, which trap pollutants near ground level). In an air quality study, the engineer and members of her team focused on cyclists who, due to their proximity to car traffic and the physical effort of riding the bike, inhale more pollution than pedestrians. Unsurprisingly, the data confirm that busy intersections are hot spots for air pollution, while green spaces dilute the concentration of pollutants.

In order to measure cyclists’ exposure to nitrogen dioxide (NO₂) and ultrafine particles (very small particles produced by combustion engines), the researchers turned to… bicycles! Since 2012, students have ridden some 400 kilometres of cycling paths every summer on bicycles fitted with sensors and a GPS. The result: maps of air pollution in relation to traffic that can be used for research purposes as well as for the development of transport and urban design policy to reduce pollution.

To share their work with the public, the McGill team also created Clean Ride Mapper, an online tool that combines modelled traffic and air quality data with a “Google Map” type algorithm, allowing cyclists to identify the least polluted route. The researchers hope to convert their prototype into a mobile application in the near future.