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Roadside Air Pollution Levels Cannot Be Ignored

Jan 02, 2009 – Leader

More frequent clear skies over our city have helped boost the government’s claim that its efforts against air pollution are succeeding. To an extent, the claim is merited. The levels of some major pollutants have indeed fallen sharply. Their roadside concentrations have been reduced by about 20 per cent in the past decade. Among these are respirable suspended particulates, nitrogen oxides and sulfur dioxide, all of which pose a major health risk.

Improved visibility also means better safety for vessels and planes; and clear blue skies are good for Hong Kong’s international image, which has been tarnished by high air pollution. No one wants to remember the Pearl of the Orient as being engulfed in choking gray smog. But picture-perfect skies do not tell the whole story. What we see is not a good indicator of what we actually breathe into our lungs.

As we report today, the number of hours that roadside monitors have clocked up above the alarm level of 100 on the air pollution index has soared in the past year. The three monitoring stations in Central, Causeway Bay and Mong Kok recorded a total of 2,007 hours, up 14 per cent from 1,760 hours in 2007. Central alone recorded 1,013 hours, a jump of 34 per cent from the year before. Causeway Bay had 402 hours, up 42.6 per cent, but Mong Kok dropped about 18 per cent with 592 hours.

The Environmental Protection Department has argued that air pollution trends are best measured by the concentrations of pollutants rather than the number of hours the API goes above 100. To be sure, unfavourable weather patterns often contribute to high API levels, but they are not necessarily the cause of a long-term trend. Admittedly, the overall decade-long trends of major pollutants have seen their concentrations either falling or levelling off. Positive contributing factors include the conversion of taxis and minibuses to LPG, the introduction of ultra-low-sulfur diesel and tighter vehicle emission standards for buses. Tougher control measures imposed by Guangdong authorities are also a significant contribution.

However, the department’s arguments are not entirely convincing. Weather patterns work both ways. Just as unfavourable conditions can push up the API, favourable ones can help bring about clear skies. More misleading is the department’s claim that frequently high API readings at roadside levels are not a good indicator of air quality trends. The department itself sets up the index as a simple way to inform the public about air quality. Surely the amount of time the index measuring roadside pollution as being above alarm levels is a highly relevant factor to consider. Otherwise, the index has no use for the public.

Many air-quality objectives the department has achieved deserve recognition. But contrary indicators may also be a warning signal. During the recent economic boom years, the number of private cars has shot up. People should be discouraged from driving in congested districts, such as by pedestrianising more roads.

More importantly, a government review panel is close to finalising a study of stronger World Health Organisation standards on air quality introduced two years ago. Despite the tougher standards, the WHO does not impose them, but encourages individual cities to adopt a realistic plan to introduce them in phases. The panel should make adopting the WHO standards a matter of urgency. A world city needs clean air and world-class standards to maintain it.

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