Chemical and stable carbon isotopic composition of PMsub2.5/sub 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 reducevehicle emissions. In order to understand the chemical characteristics ofPM_2.5 from on-road vehicle emissions in the Pearl River Delta (PRD)region and to evaluate the effectiveness of control policies on vehicleemissions, the emission factors of PM_2.5 mass, elemental carbon (EC),organic carbon (OC), water-soluble organic carbon (WSOC), water-solubleinorganic ions (WSII), metal elements, organic compounds and stable carbonisotopic composition were measured in the Zhujiang tunnel of Guangzhou, inthe 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?1respectively. 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 metalelements accounted for 15.2% of PM_2.5 emissions. Fe was the mostabundant metal element, with an emission factor of 3.91 mg vehicle?1 km?1. Emission factors of organic compounds including n-alkanes, polycyclicaromatic hydrocarbons,hopanes and steranes were 91.9, 5.02, 32.0 and 7.59 μg vehicle?1 km?1, respectively.Stable carbon isotopic composition δ13C value was ?25.0‰ onaverage. An isotopic fractionation of 3.2‰ was foundduring fuel combustion. Compared to a previous study in Zhujiang tunnel in2004, emission factors of PM_2.5mass, EC, OC, WSII exceptCl- and organic compounds decreased by 16.0 ~ 93.4%, which could beattributed to emission control policy from 2004 to 2013. However, emissionfactors of most of the metal elements increased significantly, which couldbe partially attributed to the changes in motor oil additives and vehicleconditions. There are no mandatory national standards to limit metal contentfrom vehicle emissions, which should be a concern of the government. Asnapshot of the 2013 characteristic emissions of PM_2.5 and itsconstituents from the on-road vehicular fleet in the PRD region retrieved fromour study would be helpful for the assessment of past and futureimplementations of vehicle emission control policy.