Foshan remains the Pearl River Delta's most polluted city, the latest regional air monitoring report shows.
Pollution levels there and in Dongguan and Guangzhou often exceed national air quality standards, the half-yearly figures show. The figures come from a network of 16 stations monitoring levels of sulfur dioxide, ozone, nitrogen oxides and respirable suspended particulates (RSPs).
They show Tsuen Wan in the New Territories had the third-worst record on nitrogen oxides, after Foshan and Guangdong, with levels exceeding the national standard on six days in the first half of the year. Foshan's air breached the standard on 10 days and Guangzhou's on 15.
Foshan's RSPs breached the standard on 57 days and its sulfur dioxide level was excessive on 46. The city is a centre of the ceramics industry.
The two governments set up the regional air-quality monitoring network in 2005. Foshan has consistently had the worst pollution.
Hong Kong's Environmental Protection Department said the report showed cities on the coast had better air quality than those inland.