CO concentration inside the cross harbor tunnel in Hong Kong

Carbon monoxide (CO) concentration within the Cross Harbor Tunnel in Hong Kong was investigated. Non- air-conditioned double deck buses travelling through the tunnel were used in the study to monitor the CO concentration and the distribution of CO in the tunnel. The Cross Harbor Tunnel was designed and built with a semi-transverse ventilation system during the middle of the 1960s. The quantity of fresh air was calculated according to the dilution required to keep CO from vehicular emissions within an acceptable level. The ventilation system of the tunnel was found effective in diluting this pollutant from vehicular emissions. Most CO concentrations measured in the tunnel were lower than the CO standard concentration value (30 mu L/L) in the Hong Kong Air Quality Objectives, and much lower than the original design standard. The impacts of traffic volume, vehicle speed, ventilation, piston effect, and other elements on the CO concentration in the tunnel were analyzed. A simple model for CO concentration estimation was derived and examined. It can be used to predict the CO pollution in the Cross Harbor Tunnel.