Pollution worst in western areas that are close to container terminals
Daniel Sin – SCMP – Updated on Jan 02, 2009
While many districts suffer rising levels of health-threatening pollution, residents in the east of Hong Kong Island have the cleanest air, and it has been improving over the years.
Eastern district has not recorded a reading of more than 100 on the Air Pollution Index since 2005 and, with the two other cleanest districts, Tai Po and Sha Tin, has recorded consistently improved readings.
In contrast, ambient readings at general stations in Yuen Long, Kwai Chung, Sham Shui Po, Central and Western, and Tung Chung are consistently worse than the rest of the city. In particular, in Kwai Chung last year, the number of hours when the API exceeded 100 – an alarm threshold of poor air quality – increased by 166.6 per cent from 2007.
Visibility has improved, with more blue skies creating an illusion of cleaner air. A visibility level of below 8km is defined as “reduced visibility”.
In the first 11 months of last year there were 1,654 hours of reduced visibility at the airport – an improvement of 10.4 per cent from the same period in 2007.
During the same period, there were about 1,000 hours of reduced visibility at the Observatory, the same level as last year. But experts said more clear days did not necessarily mean the air was cleaner.
“Improved visibility has little to do with the reduction of pollutant concentration, especially in areas at close range to people,” said Angus Wong Chun-yin of Friends of the Earth.
Simon Ng Ka-wing of the Hong Kong University of Science and Technology, explaining why western areas usually suffered poorer air quality, said: “These districts are close to the container terminals. The emissions from vessels are high in sulfur dioxide concentration that could explain the high readings of the API from general stations in these districts.
“Besides, the air quality in these areas is more affected by the emissions from factories in the Pearl River Delta than the rest of the city.”
One exception was the isolated Sai Kung island of Tap Mun, which suffered high pollution despite having no traffic.
“This is because Tap Mun is close to a sea route to [the Shenzhen container port of] Yantian .”
Dr Ng said the impact of high pollutant concentration could be reduced with better town planning, building designs, and energy conservation measures.
Air quality objectives adopted in 1987 define the highest concentration of pollutants that can be tolerated within a given time without causing immediate health risks.
These include sulfur dioxide, nitrogen oxides, carbon monoxide, ozone and breathable respirable suspended particles. For example, sulfur dioxide should not be allowed to exceed 800 micrograms per cubic metre of air in one hour.
Samples are collected at three roadside monitoring stations and 11 general monitoring stations that check ambient air quality in urban areas, new towns and rural areas.
The Environmental Protection Department compares the concentration of each of the pollutants against the respective air quality objective and picks the highest sub-index as the API.