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Published October 2017 | Supplemental Material
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The blue skies in Beijing during APEC 2014: A quantitative assessment of emission control efficiency and meteorological influence

Abstract

Most previous studies attributed the alleviation of aerosol pollution to either emission control measures or favorable meteorological conditions. However, our understanding of their quantitative contribution is far from complete. In this study, based on model simulation using the CMA (China Meteorological Administration) Unified Atmospheric Chemistry Environment for aerosols (CUACE/Aero), in combination with simultaneous ground-based hourly PM_(2.5) observations, we aim to quantify the relative contributions of the emission control measures and meteorology to the blue-skies seen in Beijing during the Asia-Pacific Economic Cooperation (APEC) summit held in November of 2014. A series of model simulations have been performed over Beijing-Tianjin-Hebei (BTH) region by implementing nine different emission control schemes. To investigate the relative contributions of the emission control measures and meteorology, the study period has been divided into five episodes. Overall, the CUACE/Aero model can reasonably well reproduce the temporal and spatial evolution of PM_(2.5) during APEC 2014, although the model performance varies by different time periods and regions of interest. Model results show the emission control measures on average reduced the PM+(2.5) concentration by 41.3% in urban areas of Beijing and 39.7% in Huairou district, respectively, indicating emission control plays a significant role for the blue skies observed. Among all the emission control measures under investigation, local emission control in Beijing contributed the largest to the reduction of PM_(2.5) concentrations with a reduction of 35.5% in urban area of Beijing and 34.8% in Huairou, in contrast with the vehicle emission control in Hebei that contributed the least with a reduction of less than 1%. The emission control efficiency in five episodes has been assessed quantitatively, which falls in the range of 36.2%–41.2% in urban area of Beijing and 34.9%–40.7% in Huairou, indicative of no significant episode and geographic dependence in the emission control efficiency. The emission control measures and meteorology, however, alternated to dominate the absolute reduction of PM_(2.5) concentrations. When the weather conditions are unfavorable, emission control measures outperformed meteorology with a reduction of 55.3–59.4 μg/m^3 in urban area of Beijing and 32.5–33 μg/m^3 in Huairou. Conversely, when the northwesterly winds prevailed, meteorology tends to outweigh the role of emission control in accounting for the drop of PM_(2.5). The atmospheric dilution conditions are determined through the model calculation of the mass inflow of PM_(2.5) per unit volume near the surface. Our findings have significant implications for effective planning and implementation of emission control measures.

Additional Information

© 2017 Elsevier Ltd. Received 1 May 2017, Revised 26 July 2017, Accepted 13 August 2017, Available online 15 August 2017. This work was carried out under the auspices of the Natural Science Foundation of China (Grants 91544217, 41471301, 41405006), the Ministry of Science and Technology of China (Grant 2014BAC16B01), Central Leading Local Development of Science and Technology Project in China (Grant HN 2016-149), and the Chinese Academy of Meteorological Sciences (Grants 2017Z005, 2017Y002, and 2017R001). We would like to thank Beijing Municipal Environmental Protection Monitoring Center for providing PM2.5 data. All original datasets and computer code needed to reproduce the results presented in this paper are available upon request. Last, but not least, special thanks go to the four anonymous reviewers for their valuable comments and suggestions that help improve the quality of our manuscript.

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