Characterization of particulate organics accumulated on the ceiling of vehicular tunnels in Hong Kong and Guangzhou, China

Ceiling dusts, the particulate matters accumulated on the ceiling surface of vehicular tunnels, collected from Cross-Harbor Tunnel in Hong Kong and Pear River Tunnel in Guangzhou, were analyzed for their organic compositions. Although the overall results revealed that most of the organic compounds of the ceiling dusts of both tunnels are directly derived from vehicular emission, there are significant differences in the organic content and compositions and distribution of hydrocarbon components in the ceiling dusts from these two tunnels. The ceiling dusts from the tunnel of Hong Kong were characterized by high content of organic carbon and unresolved complex matter compared to the much lower numbers in the ceiling dusts of Guangzhou. The distribution of molecular markers from CHT exhibited a 17α (H)-21β (H)-30-nor hopane (C29H) predominance (C29H>C30H) and the relative abundance of regular steranes is in an order of C27>C29>C28, whereas for the ceiling dusts from PRT, the hopanes displayed a 17α (H)-21β (H)-hopane (C30H) dominance (C29HC27>C28. It was also found that there was significant difference in the organic content in the ceiling dusts between the south- and northbound tubes of both CHT and PRT and the reasons for this require further investigation.