{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,3]],"date-time":"2026-03-03T10:18:14Z","timestamp":1772533094899,"version":"3.50.1"},"reference-count":55,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2015,11,13]],"date-time":"2015-11-13T00:00:00Z","timestamp":1447372800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>During the 2014 Asia-Pacific Economic Cooperation (APEC) Economic Leaders\u2019 Meetings in Beijing, the Chinese government made significant efforts to clear Beijing\u2019s sky. The emission control measures were very effective and the improved air quality during the APEC Meetings was called the \u201cAPEC Blue\u201d. To monitor and estimate how these emission control measures affected air quality in Beijing and its five neighboring large cities (Tianjin, Shijiazhuang, Tangshan, Jinan, and Qingdao), we compared and analyzed the satellite-retrieved Aerosol Optical Thickness (AOT) products of the pre-APEC (18\u201331 October), APEC (1\u201311 November), and post-APEC periods (11\u201331 November) in 2002\u20132014 and daily PM2.5 measurements of the three periods in 2014 on the ground. Compared with the pre- and  post-APEC periods, both ground and satellite observations indicated significantly reduced aerosol loading during the 2014 APEC period in Beijing and its surroundings, but with apparent spatial heterogeneity. For example, the peak value of PM2.5 in Beijing were around 100 \u00b5g\u2219m\u22123 during the APEC period, however, during the pre- and post-APEC periods, the peak values were up to 290 \u00b5g\u2219m\u22123. The following temporal correlation analysis of mean AOT values between Beijing and other five cities for the past thirteen years (2002\u20132014) indicated that the potential emission source regions strongly impacting air quality of Beijing were confined within central and southern Hebei as well as northern and southwestern Shandong, in correspondence with the spatial pattern of Digital Earth Model (DEM) of the study region. In addition to stringent emission control measures, back trajectory analysis indicated that the relatively favorable regional transport pattern might also have contributed to the \u201cAPEC Blue\u201d in Beijing. These results suggest that the \u201cAPEC Blue\u201d is a temporarily regional phenomenon; a long-term improvement of air quality in Beijing is still challenging and joint efforts of the whole region are needed.<\/jats:p>","DOI":"10.3390\/rs71115224","type":"journal-article","created":{"date-parts":[[2015,11,16]],"date-time":"2015-11-16T05:40:47Z","timestamp":1447652447000},"page":"15224-15243","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":24,"title":["Analysis of the 2014 \u201cAPEC Blue\u201d in Beijing Using More than One Decade of Satellite Observations: Lessons Learned from Radical Emission Control Measures"],"prefix":"10.3390","volume":"7","author":[{"given":"Ran","family":"Meng","sequence":"first","affiliation":[{"name":"Department of Geography, University of Utah, Salt Lake City, UT 84112, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4534-933X","authenticated-orcid":false,"given":"Feng","family":"Zhao","sequence":"additional","affiliation":[{"name":"Department of Geographical Sciences, University of Maryland, College Park, MD 20742, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kang","family":"Sun","sequence":"additional","affiliation":[{"name":"Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Rui","family":"Zhang","sequence":"additional","affiliation":[{"name":"Department of Geographical Sciences, University of Maryland, College Park, MD 20742, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Chengquan","family":"Huang","sequence":"additional","affiliation":[{"name":"Department of Geographical Sciences, University of Maryland, College Park, MD 20742, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jianying","family":"Yang","sequence":"additional","affiliation":[{"name":"School of Soil and Water Conservation, Beijing Forestry University, Beijing 100083, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2015,11,13]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"85","DOI":"10.1016\/j.envpol.2014.02.024","article-title":"Haze in China: Current and future challenges","volume":"189","author":"Li","year":"2014","journal-title":"Environ. 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