Parts of Hong Kong suffered serious air pollution on Sunday, with environmental authorities expecting the smog to last at least another day or until strong winds disperse the contaminants.

By evening, the Air Quality Health Index reached the “serious” level – the highest on the government’s scale – at three of the city’s 18 monitoring stations, namely North, Yuen Long and Tuen Mun stations.

Tung Chung station also recorded “very high” levels of air pollution, while the facilities in Tsuen Wan, Sha Tin, Causeway Bay and Central hit the “high” mark.

By about 10pm, the index at the Yuen Long and Tuen Mun stations fell back to “very high”, while North station recorded “high” levels of pollution.

The Environmental Protection Department said an airstream carrying high levels of background pollution – meaning contaminants not produced locally – was blowing into Hong Kong, but the fine weather with light winds was unable to disperse the pollutants.

Plenty of sunshine had also encouraged the formation of ozone, a major pollutant and greenhouse gas, over the Pearl River Delta. Ozone is one of the chemicals making up smog and can cause eye irritation and serious respiratory illness. High levels of nitrogen dioxide, another harmful chemical, had also been recorded in urban areas and by roadsides, the department said.

Dr Alexis Lau Kai-hon, chair professor of civil and environmental engineering at the Hong Kong University of Science and Technology, said the pollution was especially bad due to the weak winds.

“This time the situation is more unique, as the wind changed direction this afternoon and a northwesterly wind started to blow, carrying pollutants into Hong Kong from that direction. The area of the pollution is particularly wide,” he said.


Authorities have urged children, the elderly, and people with existing heart or respiratory illnesses to stay indoors or keep any outdoor physical activity to a minimum.


The previous cold snap had also led to an increase in pollutants, while making their dispersal more difficult – a situation common in winter, Lau said.

“I think in the next two days when the north winds start again the situation should improve,” he added. 

The department urged children, the elderly, and people with existing heart or respiratory illnesses to stay indoors or keep any outdoor physical activity to a minimum, while also requesting the general public to reduce the time spent outside.

Meanwhile, the mercury was expected to drop into single digits on New Year’s Eve and New Year’s Day, falling to a chilly 8 degrees Celsius as a cold front approached the city, the Observatory said.

Hong Kong’s first cold weather warning this winter was issued on December 17, when the mercury dropped to as low as 11.9 degrees Celsius in the urban areas.