[Physico-chemical Characteristic Analysis of PM in the Highway Tunnel in the Plateau City of Kunming].

This research aimed to determine the characteristics of the motor vehicle exhaust emissions in the plateau area. The PM was evaluated in the Caohai Tunnel of Kunming for this study by measuring the water-soluble inorganic ions, carbonaceous species, polycyclic aromatic hydrocarbons (PAHs), and inorganic elements in air samples. The results showed that the mass concentration of PM in the tunnel was about 225.65-312.84 μg·m, which is 11-14 times the PM concentration in the ambient atmosphere. The carbonaceous species were the most abundant species, constituting 35.73% of the total PM mass, followed by inorganic elements constituting about 21.78% and the water-soluble inorganic ions in the range of 4.79%-5.52%. The smallest proportion of the PM was PAH, constituting about 0.25%-0.32%. The Ca and SO concentrations were the highest among the water-soluble inorganic ions, which accounted for about 77.78%-80.17% of the total ions and from the crust source. NH and NO are relatively high, coming mainly from automobile exhausts. The 4 and 6 ring PAHs with higher molecular weight and lower volatility were the dominant components of PM in the Caohai Tunnel. The automobile exhaust contributing to PAHs in PM is very significant. The most poisonous single BaP concentration is 23-29 times higher than the state regulations exposure limit, and it has reached a hazardous level. It is obvious that there are health risks from the exposure to PM in the plateau highway tunnel. A principal component analysis (PCA) showed that the sources of road dust and automobile exhaust emission were about 61.64%, followed by mechanical wear and emissions that accounted for about 17.49% and tire wear emission sources that accounted for 9.11% of the total PM. Under the conditions of hypobaric hypoxia in the Yun-Gui plateau, there is a greater chance of incomplete combustion of motor vehicle fuels, resulting in the increase in OC and PAHs in PM emissions.