The reason why the study, which was conducted in Copenhagen, drew the troubling conclusion was because, for the cyclist, emissions dissipated into the wider atmosphere. The effect of this was to reduce exposure. However, fort the car driver the emissions are circulated around the inside of the car, increasing the concentration of the pollutants and raising the amount inhaled.
For the study, teams of two cyclists and two car drivers in two cars were given personal air samplers. The cyclists and drivers then drive for 4 hours, on two separate days, in the morning traffic of Copenhagen. After the journeys the charcoal tubes from the air-samplers were analysed. Analysis was for pollutants such as benzene, toluene, ethylbenzene and xylene. In addition, an analysis was undertaken for particles (total dust).
The research showed the concentrations of particles and xylene inside the cabin of the cars was up to four times more than in the cyclists were exposed to. This led to the conclusion that car drivers are exposed more greatly to airborne pollution than cyclists. To become more generalized, such research would need to be replicate in other global cities. A further factor will relate to the types of vehicles on the roads; here the oldest cars are the most polluting, particularly if they are diesel vehicles.
Environmental fact check: A diesel cars more polluting than petrol cars?
Diesel cars are more polluting based on their mechanism of action. Heating air in an engine produces nitrogen oxides, and thee include the toxic nitrogen dioxide, the greenhouse gas nitrous oxide, plus nitric oxide. In a petrol car, these gases can be cleaned using a three-way catalytic converter. This means petrol cars emit, on average, 30 percent less nitrogen oxides than a diesel cars.
As an example of the pollution impact from cars, The Guardian reports on a U.K. government estimate that 80 percent of harmful pollution at the roadside is coming from cars, vans and buses. The Danish research is published in the journal Science of The Total Environment. The research paper is titled “Differences in cyclists and car drivers exposure to air pollution from traffic in the city of Copenhagen.”
