Choking on success

Even environment minister Edward Yau Tang-wah would not dispute that the clear blue skies over Hong Kong in July told only part of the story about the city's air quality. Visibility was superb that month and the air pollution index fell to as low as 10 at the air quality monitoring station on Tap Mun.

But two months later, the blue sky turned grey as haze returned and spread across the whole Pearl River Delta region.

Although few would disagree that the stark contrast was linked to seasonal weather change, not everyone believes that's the sole explanation for the bad air.

Officials were quick to take credit for the blue skies of July, citing what they said was the effectiveness of existing emission control measures. Thanks to the conversion of taxis and minibuses to LPG and the introduction of ultra-low sulfur diesel and tighter vehicle emission standards, annual average concentration levels of nitrogen oxides and particulates at the roadside have fallen by 19 per cent and 13 per cent respectively in the past eight years.

However, their critics said an overemphasis on the role of weather in determining air quality showed the need for tougher measures. The weather factor also removed the incentive for the public to take part in a clean up.

Sceptics said the blue skies were related to regional pollution factors and separate from the issue of clean air at the roadside, which is determined more by transport and the urban landscape.

'The haze obscuring the blue sky is more a visual and image problem and they should be tackled. But a real improvement in air quality should start from the roadside [as it] has the biggest impact on people's health,' said Professor Alexis Lau Kai-hon, an atmospheric scientist at the University of Science and Technology.