Decrease of VOC emissions from vehicular emissions in Hong Kong from 2003 to 2015: Results from a tunnel study

Vehicular emissions are one of major anthropogenic sources of ambient volatile organic compounds (VOCs) in Hong Kong. During the past twelve years, the government of the Hong Kong Special Administrative Region has undertaken a series of air pollution control measures to reduce vehicular emissions in Hong Kong. Vehicular emissions were characterized by repeated measurement in the same roadway tunnel in 2003 and 2015. The total net concentration of measured VOCs decreased by 44.7% from 2003 to 2015. The fleet-average VOC emission factor decreased from 107.1 ± 44.8 mg veh−1 km−1 in 2003 to 58.8 ± 50.7 mg veh−1 km−1 in 2015, and the total ozone (O3) formation potential of measured VOCs decreased from 474.1 mg O3 veh−1 km−1 to 190.8 mg O3 veh−1 km−1. The emission factor of ethene, which is one of the key tracers for diesel vehicular emissions, decreased by 67.3% from 2003 to 2015 as a result of the strict control measures on diesel vehicular emissions. Total road transport VOC emissions is estimated to be reduced by 40% as compared with 2010 by 2020, which will be an important contributor to achieve the goal of total VOC emission reduction in the Pearl River Delta region. The large decrease of VOC emissions from on-road vehicles demonstrates the effectiveness of past multi-vehicular emission control strategy in Hong Kong.