Carbon monoxide levels in popular passenger commuting modes traversing major commuting routes in Hong Kong

Vehicle exhaust is a major source of air pollution in metropolitan cities. Commuters are exposed to high traffic-related pollutant concentrations. Pub lic transportation is the most popular commuting mode in Hong Kong and ther e are about 10.8 million passenger trips every day. Two-thirds of them are road commuters. An extensive survey was conducted to measure carbon monoxid e in three popular passenger commuting modes, bus, minibus, and taxi, which served, respectively, 3.91 million. 1.76 million and 1.31 million passenge r trips per day in 1998. Three types of commuting microenvironments were se lected: urban-urban, urban-suburban and urban-rural. Results indicated that in-vehicle CO level increased in the following order: bus, minibus and tax i. The overall average in-vehicle CO level in air-conditioned bus, minibus and taxi were 1.8, 2.9 and 3.3 ppm, respectively. The average concentration level difference between air-conditioned buses (1.8 ppm) and non-air-condi tioned buses (1.9 ppm) was insignificant. The fluctuation of in-vehicle CO level of non-air-conditioned vehicle followed the variation of out-vehicle CO concentration. Our result also showed that even in air-conditioned vehic les, the in-vehicle CO concentration was affected by the out-vehicle CO con centration although there exists a smoothing out effect. The in-vehicle CO level was the highest in urban-suburban commuting routes and was followed b y urban-urban routes. The in-vehicle CO level in urban-rural routes was the lowest. The highest CO level was recorded after the vehicle traversed thro ugh tunnel. The average CO exposure of a commuter in tunnel can be 2-3 time s higher than that at the other roads. The CO exposure level of public road transportation commuters in Hong Kong was lower than most other cities. Fa ctors governing the CO levels were also discussed. (C) 2001 Elsevier Scienc e Ltd. All rights reserved.