Exposure level of carbon monoxide and respirable suspended particulate in public transportation modes while commuting in urban area of Guangzhou, China

This study examined commuter exposure to respirable suspended particulate (PM10 and PM2.5) and carbon monoxide (CO) in public transportation modes in Guangzhou, China. During the sampling period, a total of 80 CO, 80 PM10 and 56 PM2.5 samples were conducted in four popular commuting modes (subway, air-conditioned bus, non-air-conditioned bus and taxi) while running in typical urban routes. The results show that the PM10 as well as CO level is greatly influenced by the mode of transport. The highest mean PM10 and CO level was obtained in a non-air-conditioned bus (203 μg m−3) and in an air-conditioned taxi (28.7 ppm), respectively. Noticeably, the exposure levels in subway are lower than those in the roadway transports. The ventilation condition of the transport is also a crucial factor affecting the in-vehicle level. There was statistically significant difference of PM10 (p<0.01) and CO (p<0.01) level in taxi and PM10 (p<0.01) level in bus between natural and mechanical ventilation. In this study, the effect of driving time has minor impact on the in-vehicle level. The exposure levels were only slightly lower in afternoon non-peak hour than in evening peak hour. This is related to the fact that the road traffic in the selected urban routes is dominated by the extensive use of public transports, which provide service at regular intervals regardless of the time of day. The PM2.5 inter-microenvironment variation is similar to the pattern of PM10. The PM2.5 to PM10 ratio in the transports was high, ranging from 76% to 83%. The poor vehicle emission controls, poor vehicle maintenance, plus the slow moving traffic condition with frequent stops are believed to be the major causes of high in-vehicle levels in some public commuting trips.