Many studies have been carried out in different parts of the world to try to gain a better understanding of personal exposure to air pollutants while commuting by different modes [5-8], aided by the recent development of portable air quality monitoring technology. Although the results from such studies are frequently complex and sometimes contradictory due to a large number of confounding factors [9], typically they show that the mean concentrations of air pollutants pedestrians and cyclists are exposed to are lower than those experienced by car drivers and bus passengers [10,11]. It is believed that this is due to.
