Particulate matter emissions from on-road vehicles in a freeway tunnel study

Particulate matter, including coarse particles (PM2.5–10, aerodynamic diameter of particle between 2.5 and 10 μm) and fine particles (PM2.5, aerodynamic diameter of particle lower than 2.5 μm) and their compositions, including elemental carbon, organic carbon, and 11 water-soluble ionic species, and elements, were measured in a tunnel study. A comparison of the six-hour average of light-duty vehicle (LDV) flow of the two sampling periods showed that the peak hours over the weekend were higher than those on weekdays. However, the flow of heavy-duty vehicles (HDVs) on the weekdays was significant higher than that during the weekend in this study. EC and OC content were 49% for PM2.5–10 and 47% for PM2.5 in the tunnel center. EC content was higher than OC content in PM2.5–10, but EC was about 2.3 times OC for PM2.5. Sulfate, nitrate, ammonium were the main species for PM2.5–10 and PM2.5. The element contents of Na, Al, Ca, Fe and K were over 0.8 μg m−3 in PM2.5–10 and PM2.5. In addition, the concentrations of S, Ba, Pb, and Zn were higher than 0.1 μg m−3 for PM2.5–10 and PM2.5. The emission factors of PM2.5–10 and PM2.5 were 18 ± 6.5 and 39 ± 11 mg km−1-vehicle, respectively. The emission factors of EC/OC were 3.6/2.7 mg km−1-vehicle for PM2.5–10 and 15/4.7 mg km−1-vehicle for PM2.5 Furthermore, the emission factors of water-soluble ions were 0.028(Mg2+)–0.81(SO42−) and 0.027(NO2−)–0.97(SO42−) mg km−1-vehicle for PM2.5–10 and PM2.5, respectively. Elemental emission factors were 0.003(V)–1.6(Fe) and 0.001(Cd)–1.05(Na) mg km−1-vehicle for PM2.5–10 and PM2.5, respectively.