This study investigated the passenger exposure to particulate matter (PM) in long-distance buses in Taiwan. PM and CO2 were measured in thirty buses traveling between Taipei and Tainan. The results indicated that average in-cabin PM levels were below the guidelines or standards suggested by Taiwan and other countries. Cigarette smoking revealed no effect on in-cabin PM2.5 level. However, since only one cigarette was lit per journey, the effect might be different if more cigarettes were lit in bus cabins. Opening windows was found to affect in-cabin PM2.5 and PM2.5/PM10 ratios may be elevated. Moreover, the PM10 level from air monitoring stations did not reflect the true passenger exposure to PM10. This study concludes that PM levels in long-distance buses is lower than those in other studies of urban buses, as a result of faster driving speed, non-stop driving pattern, and highway surroundings. Keeping windows closed on long-distance buses can minimize passenger exposure to PM2.5. Conversely, high in-cabin CO2 levels may occur if opening window is minimized when air change rate is low. This study suggests that long-distance buses should increase their air exchange rates to reduce CO2 levels and install particle filters with high removal efficiency to lower in-cabin PM levels.Practical Implications
The PM levels in the long-distance buses running on highways are lower than those observed in city buses. Opening window in the long-distance buses would result in higher in-cabin PM levels but may effectively reduce in-cabin CO2 levels, which accumulate over the journey of long hours. Increase of air exchange rate and installation of filters with high PM removal efficiency in ventilation system are suggested to improve air quality in the cabin of long-distance buses.