OK. Actually the reason I felt it was unlikely to be correct was that I have lived in both river deltas (a year each in Shanghai, Shenzhen, Zhuhai) as well as t

OK. Actually the reason I felt it was unlikely to be correct was that I have lived in both river deltas (a year each in Shanghai, Shenzhen, Zhuhai) as well as travelled extensively (Suzhou, Yangzhou, upper Yangtse, Jiangmen, etc.) and suspect given the manufacturing and residential density and geographic expanse of the lower PRD, it should have significant garbage versus Yangtse. How was the data gathered? Satellite? When was it gathered? The 2017 paper probably uses 2015 or earlier data, there have been substantial improvements on environmental issues in the PRD region (really China-wide) of late, but I'd still be surprised if it's substantially cleaner in plastic refuse terms than the Yangtse.