On-road measurements of pollutant concentration profiles inside Yangkou tunnel, Qingdao, China.

To obtain physical properties of pollutant concentrations encountered by vehicle commuters during travelling Yangkou tunnel (7.76 km) of Qingdao City, particle concentration measurements are accompanied by the measurements of gaseous species (CO and CO2 ). The field campaigns are on-road conducted from April 26 to September 23, 2014. Results demonstrate that the mean particle number concentrations observed within the tunnel at the normal traffic volume are 1.15 × 105 and 1.24 × 105  particles cm-3 for the southbound and northbound trip, respectively. Furthermore, the significance level of traffic volume to particle number concentration is analyzed by multivariate regression model. And a high correlation between pollutant concentrations and traffic intensity has been demonstrated. Consequently, the fuel-based emission factors of pollutants inside the tunnel are calculated and the personal exposures are derived. In addition, the profile of particle number concentration exhibits distinct dilution features between the exit of northbound bore and the exit of southbound bore. The explanation is attributed to the different long uphill trip within the tunnel. Results in this study offer meaningful understanding to explore the nature of pollutants within long tunnels.