Chemical composition of PM_2.5 from two tunnels with different vehicular fleet characteristics

The chemical compositions of PM_2.5 including OC, EC, water soluble ions, elements, and organic components such as polycyclic aromatic hydrocarbons (PAHs), hopanes, and steranes, emitted in Wuzushan (WZS) and Kuixinglou (KXL) tunnels were determined. WZS tunnel is a major route for diesel vehicles traveling, while KXL tunnel has limited to diesel vehicles. The results showed that the proportions of the different constituents of PM_2.5 in the Wuzushan (WZS) tunnel were OC (27.7%), EC (32.1%), elements (13.9%), and water soluble ions (9.2%). Whereas the chemical profile of PM_2.5 in the Kuixinglou (KXL) tunnel was OC (17.7%), EC (10.4%), elements (8.90%), and water soluble ions (8.87%). The emission factors (EFs) of PM_2.5 and proportions of SO₄^2- and Pb were decreased by vehicle emission standards and fuel quality policy in China, and the higher molecular weight PAHs (4+5+6 rings) were more abundant than the lower molecular weight PAHs (2+3 rings) in the two tunnels. The proportions of 17A(H)-21B(H)-30-Norhopane and 17A(H)-21B(H)-Hopane in the hopane and sterane were not dependent on the vehicles types. In addition, specific composition profiles for PM_2.5 from gasoline-fueled vehicles (GV) and diesel-fueled vehicles (DV) emissions were drafted, which indicated that OC (0.974mg·veh^-1·km^-1) was the most abundant component in PM_2.5, followed by Fe, Cl^-, and Mg for GV. The relative proportions of the different constituents in the PM_2.5 for DV were EC (35.9%), OC (27.2%), elements (12.8%), and water soluble ions (11.7%). Both the PM_2.5 EFs and EC proportions in DV were higher than those in GV, and the HMW PAHs were the dominant PAHs for both GV and DV. The PM_2.5 emissions from the vehicles in Yantai were 581±513tons to 1353±1197tons for GV, and 19,627±2477tons to 23,042±2887tons for DV, respectively.