Emission factors of volatile organic compounds (VOCs) based on the detailed vehicle classification in a tunnel study.

In order to obtain VOCs emission characteristics and emission factors from vehicle, a tunnel experiment was conducted in the Fu Gui Mountain Tunnel in Nanjing, China. The tunnel is located in the middle of city, with total length of 480m and speed limit of 50km/h. The studied vehicle fleet was composed of 87% light duty vehicles and 13% heavy duty vehicles (liquefied natural gas bus, LNGB). The emerging radio frequency identification (RFID) technology was used to divide fine vehicles type including China I, China II, China III, China IV, China V and LNGB. Ambient air samples (4-h averages) were collected inside the tunnel using 3.2L stainless-steel canisters. Samples collected in the canisters were analyzed for 97 individual VOCs using high-resolution GC-MS in the laboratory. The average tunnel emission factor for the collective light-duty vehicles was 160.79±65.94mg/(km∗veh), and for the China I, China II, China III, China IV and China V vehicles, it was 632.07±259.44, 450.35±184.85, 205.42±84.32, 118.51±48.65, and 110.61±45.4mg/(km∗veh), respectively. The average emission factor for heavy-duty vehicles was 358.02±124.86mg/(km∗veh). Ethane, isopentane, propane, ethylene, toluene, propylene and 2,3-dimethylbutane were the most common VOC species in vehicle emissions. The total O3 formation potential was 373.88mg∗O3/(km∗veh) in the tunnel. Ethylene, propylene, m/p-xylene, toluene, and isopentane were the largest contributors to O3 production. Compared with previous studies, fuel quality increased from China II-FQ to China IV-FQ levels, while the BTEX emission levels exhibited a decreasing trend.