Air pollution levels in some districts were about as bad as they can be for a second time in five days as smog blanketed Hong Kong yesterday.
But pollution is expected to ease in the next couple of days as an intense northeast monsoon starts to affect the south China coast, according to the Hong Kong Observatory.
At 5.30pm yesterday health risks from air pollution were “serious” – the highest level in the five-tier Air Quality Health Index – at general stations in Yuen Long, Tuen Mun and Tung Chung.
Pollution was “very high” at the Central, Eastern, Kwai Chung, Tsuen Wan, Tseung Kwan O, Tai Po and Tap Mun general stations and at roadside stations in Causeway Bay, Central and Mong Kok.
Children, the elderly and people with heart or respiratory illnesses are advised to avoid physical exertion and outdoor activities when the very high level is reached.
Environmental Protection Department experts explained that hazy conditions with sunny periods and light winds hindered the dispersal of pollutants in Hong Kong and beyond.
Also, sunshine enhances photo-chemical smog activity and the formation of ozone and fine particulates. And a high level of ozone promotes the formation of nitrogen dioxide.
World Green Organization chief executive William Yu Yuen-ping attributed the poor air quality to smog in south China that has blown to Hong Kong.
He said areas such as Yuen Long and Tuen Mun near the Pearl Delta were affected to a greater extent.
But Loong Tsz-wai, community relations manager of the Clean Air Network, pointed to the western part of Hong Kong where the level of nitrogen dioxide was elevated yesterday while the level of ozone was not so high.
“Nitrogen dioxide is due to vehicle emissions, while the weather made it difficult to disperse,” Loong said.
“If it was regional air pollution the level of ozone would be high too.”
So the high level of nitrogen dioxide was produced by traffic in Hong Kong and had nothing to do with the mainland, Loong added.
Wednesday also saw major health risks from air pollution in various districts.