资源环境科技发展态势分析平台

Vehicle emissions are a major source of air pollution in urban areas and thus greatly impact air quality in the megacity Beijing. Various vehicle emission control policies have been implemented at great cost, but there is a lack of appropriate methods to evaluate the effectiveness of such policies. Here we developed a wavelet transform method (WTM) to evaluate the effectiveness of vehicle emission control policies during the 2014 Asia-Pacific Economic Cooperation (APEC) summit, taking advantage of high-time-resolution mobile measurements of NO, NOx, BC, CO, SO2, and O-3 made around the 4th Ring Road of Beijing. The WTM decomposed on-road mobile measurements into high- and low-frequency components, where the former represents immediate vehicle emissions, and the latter represents the atmospheric background in addition to accumulated on-road emissions. The high-frequency component of the WTM (CH_freq :), which represents the concentrations of pollutants from vehicle emissions (C-veh.), was used to evaluate the changes in vehicle emission intensity in the full-APEC period (3-12 November 2014) relative to the pre-APEC (28 October to 2 November 2014) and post-APEC (13-22 November 2014) periods, during which different vehicle emission control policies were implemented. Our results suggest that the C-veh. of NO, NOx, BC, and CO in the full-APEC period were 19.4 %, 17.7 %, 0.0 %, and 50.0% lower, respectively, than those in the pre-APEC period during daytime and were