Via googling, just come across summary of paper on recent study on air pollution across Pearl River Delta, inc Hong Kong:
Quote:
Fine particulate matter (PM2.5) was measured for 4 months during 2002-2003 at seven sites located in the rapidly developing Pearl River Delta region of China, an area encompassing the major cities of Hong Kong, Shenzhen and Guangzhou. The 4-month average fine particulate matter concentration ranged from 37 to 71 ug/m3 in Guangdong province and from 29 to 34 ug/m3 in Hong Kong. Main constituents of fine particulate mass were organic compounds (24-35% by mass) and sulfate (21-32%). … The vicinity of Guangzhou is determined to be a major source area influencing regional concentrations of PM2.5 … In addition, it appears that sources outside of the Pearl River Delta contribute a significant fraction of overall fine particulate matter in Hong Kong and Guangdong province. This is evident in the relatively high PM2.5 concentrations observed at the background sites of 18 ug/m3 (Tap Mun, southerly flow conditions) and 27 ug/m3 (Conghua, northerly flow conditions).
Source areas and chemical composition of fine particulate matter in the Pearl River Delta Region of China Note that even the figure for Tap Mun during southerlies is significant, when look at new US study showing fine particulates boost risks of heart attacks and strokes: Air Pollution Linked to Heart Deaths Risk May Be Higher Than Previous Studies Suggest