Who is most susceptible to urban air pollution: pedestrian, cyclist, car driver or bus passenger? Why?

Research of the university of Hasselt, where a group of people carried a personal black carbon measuring device during all their movements for a week, pointed out that when traveling, people are exposed to 2 to 5 times the air pollution in comparison to when staying at home. The highest concentrations were measured for car drivers and passengers of both cars and busses. The concentrations to which people were exposed when moving on foot or by bike were  about 50% lower. The lowest concentrations were observed in trains. Of course, a lot depends on the trajectory chosen for the relocation. The eventual amount of pollution inhaled is also dependent on your respiratory rate and the time spent relocating. If you calculate the dose inhaled (or pollution per minute), it appears the more active persons (pedestrians and cyclists) inhale a dose about twice as high as the more passive ones (moving by car or bus). This is caused by the higher breathing frequency of cyclists and pedestrians. When moving on foot or by bike, it is advised to do so along streets with as little traffic as possible.

Source: article university of Hasselt