Updated on Dec 29, 2008 – SCMP
I refer to the letter by Richard Fielding (“Lack of will to fight pollution”, December 19).
The government is determined to improve Hong Kong’s air quality. On the home front, we have implemented comprehensive measures to control our emissions at source. We have capped the emissions of the power plants and required the use of ultra-low-sulfur diesel across all industrial and commercial processes. We are controlling products that contain volatile organic compounds in a manner similar to California. Our control on vehicular fuel and emission standards is on a par with the most stringent European requirements. To address the regional smog issue, we are working with the Guangdong provincial government to reduce the emissions of four key air pollutants in the region by 20 per cent to 55 per cent by 2010.
We are reviewing our air quality objectives taking into account the latest international developments including the air quality guidelines published by the World Health Organisation.
Professor Fielding raised concern about the relationship between air pollutant concentrations and the air pollution index (API). Like many other overseas API systems, our API is computed by – converting the concentrations of various pollutants over different averaging times ranging from one hour to 24 hours into sub-indices by comparing the concentrations with the respective one hour to 24-hour air quality objectives; and, taking the highest of the sub-indices as the API for a station at that hour.
The air quality objectives for respirable suspended particulates (RSP) are based on an averaging time of 24 hours instead of one hour, due to the lack of scientific evidence with respect to the exposure-response relationship for RSP over a period as short as one hour. Hence the API for RSP is computed based on moving 24-hour average concentrations instead of one-hour concentrations.
The API is derived from the actual pollutant concentrations and therefore bears direct relationship with the state of air quality. On December 15, the day mentioned by Professor Fielding, the API for the general stations was on the upper side of the high band, and the roadside API was up to 104 at the Central roadside station in the afternoon. Both readings indicated that the pollution level on that day was considered high or very high.
To make the API more useful to the public we have engaged a team of leading academics from local universities to review our API system and draw up its recommendations for improvement. The review will be completed within 2009.
Dave Ho, principal environmental protection officer, Environmental Protection Department