Abstract
Abstract. 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 O3 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 (Cveh.), 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 Cveh. 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 50.0 %, 47.3 %, 62.5 %, and 50.0 % lower than those in the post-APEC period during daytime. The Cveh. of NO, NOx, BC, and CO in the full-APEC period were 65.3 %, 65.4 %, 14.3 %, and 50.0 % lower than those in the post-APEC period during night-time. These results indicate that the vehicle emission control policies implemented during the full-APEC period were effective. Using on-road mobile measurements in combination with the WTM, we developed a new method for the evaluation of pollution control policies.
Highlights
Due to socioeconomic development and fast urbanization, vehicle usage in megacities has increased rapidly, resulting in increasing on-road emissions of air pollutants
We carefully investigated the time series of the wavelet transform (WT) results and found that an eight-level decomposition could describe the characteristics of on-road vehicle emissions correctly (Westerdahl et al, 2009; Han et al, 2014)
We developed and validated a wavelet transform method (WTM) to evaluate the effectiveness of vehicle emission control policies implemented during Asia-Pacific Economic Cooperation (APEC)
Summary
Due to socioeconomic development and fast urbanization, vehicle usage in megacities has increased rapidly, resulting in increasing on-road emissions of air pollutants. On-road mobile measurements can be used to obtain the spatial and temporal distributions of air pollutants with high time resolution They have been widely used in the evaluation of air pollution control policies (Wang et al, 2009) and regional transport into megacities and over a large-scale area (Wang et al, 2011; Zhu et al, 2016). The WT can be used to extract the narrow and sharp spikes in time series of air pollutants by decomposing the signals of on-road mobile measurements to different frequencies, and, in theory, the WT can be used to evaluate the effectiveness of vehicle emission control policies. 3.3, we used the WTM to evaluate the effectiveness of vehicle emission control policies implemented during the 2014 APEC summit in Beijing as a case study.
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