Characteristics of particulates and gaseous pollutants in a highway tunnel

Characteristics of air pollutants in a highway tunnel were studied in Osaka, Japan. The size distributions and concentrations of elemental carbon (EC) and organic carbon (OC) were measured. The results demonstrated that EC was the predominant constituent of particulates in the tunnel, which accounted for 71% by mass of the particulate matter (PM) of less than 2 μm in aerodynamic diameter. EC concentration increased linearly with increase in diesel traffic volume and the coefficient of correlation was found to be at a significant level (r=0.93, p<0.001). In contrast, OC size distribution was bimodal with peaks in the size ranges of less than 1 and 2–10 μm and not clearly dependent on diesel traffic volume. For the gaseous matter, nitrogen monoxide (NO) was found to be the major component of NOx (over 90%) and its concentration was proportional to the traffic volume of diesel vehicles (r=0.82, p<0.001). The concentrations of carbon monoxide (CO) and carbon dioxide (CO2) in the tunnel were found, by multi-regression analysis, to be dependent on both diesel and gasoline-powered vehicles.