Typhoon Saola helped push Hong Kong's air pollution index to the highest level ever recorded outside of extreme circumstances yesterday, with Central and Yuen Long suffering the worst readings.
With the Environmental Protection Department warning that pollution would remain severe today as the typhoon approaches Taiwan, an anti-pollution group warned people against going outdoors.
At 3pm the air quality monitoring station in Yuen Long recorded a reading of 202, with ozone the major pollutant. It matched the previous highest, registered in Tap Mun in 2008.
The only time readings have ever been higher was in March 2010, when a sandstorm originating in northern China dumped fine particles over the city, pushing readings off the top of the 500-point chart.
The roadside monitoring station at Central recorded the highest roadside index, at 193, with very high concentrations of nitrogen dioxide.
A spokesman for the Environmental Protection Department said: 'Under the influence of the outer subsiding air of Typhoon Saola, the weather has been fine and the wind light in the South China region.
'The intense sunshine and high temperature have enhanced photochemical smog formation, resulting in elevated ambient ozone levels.'
Roadside pollution was severe because, with virtually no wind, pollutants from motor vehicles were trapped. The index at nine of the 11 general monitoring stations and all three roadside stations was over 100, considered a 'very high' level of pollution, at various times.
Typhoon Saola was centred about 310 kilometres northeast of Gaoxiong in southern Taiwan last night. It was forecast to move towards Fujian province. The weather in Hong Kong will remain hot today, with thunderstorms later.
Erica Chan, campaign manager for the Clean Air Network, urged the government to take urgent action to implement anti-pollution measures, such as setting up low-emission zones and a scheme to scrap old commercial diesel vehicles.
'Although a major contributor to the high levels of air pollution is external weather forces, we should note that locally generated vehicle exhaust emissions are the real root of the problem,' she said. People should avoid going outdoors, Chan said.
The Airport Authority said 22 flights between Taipei and Hong Kong were cancelled yesterday, with 10 others delayed.
Eight Hong Kong Airlines flights between the city and Taipei yesterday and today were cancelled, plus four to and from Taichung. The airline, which was criticised for its handling of delays after Severe Typhoon Vicente hit Hong Kong last month, will waive rebooking fees for passengers who had tickets for flights to Taiwan between today and Sunday and want to change their travel plans.
Cathay Pacific and Dragonair suspended all flights to and from Taipei from 6pm yesterday to noon today.