Commuter exposure to particulate matter in public transportation modes in Hong Kong

This study examined commuter's exposure to respirable suspended particulate matters while commuting in public transportation modes. The survey was conducted between October 1999 and January 2000 in Hong Kong. A total of eight public transportation modes, that are bus, tram, public light bus, taxi, ferry, Kowloon-Canton Railway, Mass Transit Railway and Light Rail Transit, were selected in the study. They were grouped into four categories: (T1) railway transport; (T2) non-air-conditioned roadway transport; (T3) air-conditioned roadway transport and (T4) marine transport. Both PM10and PM2.5levels were investigated. The results indicate that the particulate level is greatly affected by the mode of transport as well as the ventilation system of the transport. The overall average PM10concentration level in T2 (147μgm-3) is the highest and is followed by T4 (81μgm-3) and T3 (65μgm-3). The PM10level in T1 (50μgm-3) is the lowest. Notably, the commuter exposure in tram (175μgm-3) is the highest among all the monitored commuting modes. Commuting modes such as railway and air-conditioned vehicle are recommended as a substitute for non-air-conditioned vehicle. The PM2.5to PM10ratio in transports ranged from 63% to 78%. Higher PM2.5to PM10ratio is found in vehicles with air-conditioning system. For the double deck vehicle, higher PM10level has resulted in the lower deck. The average upper-deck to lower-deck PM10ratio is 0.836, 0.751 and 0.738 in air-conditioned bus, non-air-conditioned bus and non-air-conditioned tram, respectively. Typical concentration profiles in different transports are also presented.