Relationship between air pollution in Hong Kong and in the Pearl River Delta region of south China in 2003 and 2004: An analysis

Air pollution in the Pearl River Delta (PRD) region of south China, which is one of the four regions in China most heavily affected by haze, is found to correlate with that of Hong Kong, indicating the regional nature of the Hong Kong problem. Of the 10 territory-wide episode days occurring in Hong Kong in 2003 and 2004, 3 of them coincide with the most polluted days of the month in the PRD. On two other episode days, the most polluted days in the PRD occurred within 2 days of the Hong Kong episodes. The air pollution trends of the PRD cities and Hong Kong are found to resemble each other more under certain meteorological conditions than others, notably when a tropical storm is positioned at the Luzon Strait between Taiwan and Luzon in the Philippines, and the entire PRD, including Hong Kong, is equally affected by it, resulting in photochemical events. During this time, Hong Kong is downwind of nearly all pollution sources in the region. At other positions of the storm, the eastern part of the PRD is often affected more significantly. In winter episodic conditions, which occur when weak anticyclones prevail over south China, local meteorological factors, namely, inversions and sea-breeze convergences, are believed to contribute to the temporal difference of the pollution peaks in Hong Kong and the rest of the PRD.