Chemical and stable carbon isotopic composition of PM_(2.5) from on-road vehicle emissions in the PRD region and implications for vehicle emission control policy

摘要

Vehicle emissions are a major source of urban air pollution. In recent decade, the Chinese government has introduced a range of policies to reduce vehicle emissions. In order to understand the chemical characteristics of PM_(2.5) from on-road vehicle emissions in the Pearl River Delta (PRD) region and to evaluate the effectiveness of control policies on vehicle emissions, the emission factors of PM_(2.5) mass, elemental carbon (EC), organic carbon (OC), watersoluble organic carbon (WSOC), water-soluble inorganic ions (WSII), metal elements, organic compounds and stable carbon isotopic composition were measured in the Zhujiang tunnel of Guangzhou, in the PRD region of China in 2013. Emission factors of PM_(2.5) mass, OC, EC and WSOC were 92.4, 16.7, 16.4 and 1.31 mg vehicle~(-1) km~(-1) respectively. Emission factors of WSII were 0.016 (F~-)~4.17 (Cl~-) mg vehicle~(-1) km~(-1), contributing about 9.8% to the PM_(2.5) emissions. The sum of 27 measured metal elements accounted for 15.2% of PM_(2.5) emissions. Fe was the most abundant metal element, with an emission factor of 3.91 mg vehicle~(-1) km~(-1). Emission factors of organic compounds including n-alkanes, polycyclic aromatic hydrocarbons, hopanes and steranes were 91.9, 5.02, 32.0 and 7.59 μg vehicle~(-1) km~(-1), respectively. Stable carbon isotopic composition δ~(13)C value was ~25.0‰ on average. An isotopic fractionation of 3.2‰ was found during fuel combustion. Compared to a previous study in Zhujiang tunnel in 2004, emission factors of PM_(2.5) mass, EC, OC, WSII except Cl~- and organic compounds decreased by 16.0~93.4 %, which could be attributed to emission control policy from 2004 to 2013. However, emission factors of most of the metal elements increased significantly, which could be partially attributed to the changes in motor oil additives and vehicle conditions. There are no mandatory national standards to limit metal content from vehicle emissions, which should be a concern of the government. A s