Comparisons of commuter's exposure to particulate matters while using different transportation modes

This study compared commuters' exposures to particulate matter (PM) while using motorcycles, cars, buses, and the mass rapid transit (MRT) on the same routes in Taipei, Taiwan. Motorcycle commuters who had the shortest travel time (28.4 ± 4.2 min) were exposed to the highest concentrations of PM10 (112.8 ± 38.3 μg/m3), PM2.5 (67.5 ± 31.3 μg/m3), and PM1.0 (48.4 ± 24.7 μg/m3) among four commuting modes. By contrast, car commuters were exposed to the lowest PM concentrations and had the second shortest travel time among them. Motorcycle commuters' high trip-averaged PM concentrations and bus commuters' long commuting time (43.1 ± 5.1 min) resulted in their high whole-trip PM exposures. Size fractions of PM were relatively consistent across PM exposures of the four commuting modes with fine particles (PM2.5) contributing to 53–60% of PM10 and submicron particle (PM1) contributing to 39–43% of PM10. Motorcycles idled at traffic lights and bus doors opened at stops increased commuters' PM exposures. Fixed-site monitoring data explained well the variation of whole-trip PM10 exposure of car (r2 = 0.63) and MRT (r2 = 0.52) commuters, and of whole-trip PM2.5 exposure of car (r2 = 0.76), MRT (r2 = 0.73) and motorcycle (r2 = 0.64) commuters in regression analyses. The coefficients (slopes) of regression between fixed-site monitoring data and PM2.5 exposures were less than 1 for car and MRT commuters but greater than 1 for motorcycle commuters. In conclusion, proximity to traffic emissions contributes to a person's high PM exposure during his or her daily commute. This proximity occurs when people use motorcycles on roads and when bus/MRT commuters walk or wait along commuting routes. Fixed-site air monitoring data can under-estimate motorcycle commuters' PM2.5 exposures but over-estimate car and MRT commuters' PM2.5 exposures.