Traditional Chinese Simplified Chinese Email this article Government Homepage
LCQ2 : Comparison of air quality between Hong Kong and other cities
************************************************************

    Following is a question by the Hon Lui Ming-wah and a reply by the Secretary for the Environment, Transport and Works, Dr Sarah Liao, in the Legislative Council meeting today (December 20) :

Question:

     It has been reported that some individuals in the political and financial sectors and academics recently indicated that their family members had moved to live in other places as the problem of air pollution was serious in Hong Kong.  In addition, some securities companies have lowered the investment ratings of the shares of three local real estate companies because of Hong Kong's air pollution problem, and have recommended instead the shares of the properties sector in other places.  In this connection, will the Government inform this Council:

(a)  whether it knows the latest average air pollution indices ("APIs") and the average life expectancy in various famous overseas cities, namely, New York, San Francisco, Washington D.C., Chicago, London and Singapore; and

(b)  whether the APIs currently adopted in Hong Kong can be compared to the APIs adopted in the above cities; if so, of the results of the comparison; if not, the reasons for that?

Reply:

Madam President,

     Before replying to the specific questions raised by the Hon Lui Ming-wah, I would like to explain how air quality standards are set and how air pollution is measured internationally.  There is currently no uniform international air quality standard.  Although the World Health Organization (WHO) has recommended guidelines on air quality, it clearly points out that individual countries and regions should strike a balance among factors such as health impact, technical feasibility, social and political situation, as well as economic considerations when formulating their statutory air quality standards.  Therefore, individual countries and regions should set their respective air quality standards in the light of the local situation.  For example:

(i)  the 24-hour limit values of sulphur dioxide are 20£gg/cubic metre under WHO standard, 365£gg/cubic metre under the United States (US) standard, 350£gg/cubic metre under Hong Kong standard and 125£gg/cubic metre under European Union (EU) standard.  Although the EU has set a very strict standard, it also allows a higher exceedance rate (3 exceedances per year) while only 1 exceedance is allowed per year for both the US and Hong Kong;

(ii)  the 1-hour limit values of nitrogen dioxide are 200£gg/cubic metre under WHO and EU standards, 150£gg/cubic metre under Norway standard and 300£gg/cubic metre under Hong Kong standard.  The exceedances allowed by the EU and Norway are 18 and 8 per year respectively, which are far higher than the 3 exceedances per year allowed in Hong Kong; and

(iii)  the 24-hour limit values of respirable suspended particulates (RSP) (PM10) are 50£gg/cubic metre under WHO and EU standards, 150£gg/cubic metre under US standard and 180£gg/cubic metre under Hong Kong standard.  While the exceedance allowed by EU is 35 per year, the US and Hong Kong allow only 1 exceedance per year respectively.

     There are no uniform methods for the computation and publication of air pollution indices (APIs) internationally.  How APIs are published and computed varies substantially across cities.

     Madam President, in the light of the constraints mentioned above, we would respond to Hon Lui Ming-wah's question with reference to information published by different places as follows:

(a)  We cannot find the average APIs of New York, San Francisco, Washington D.C., Chicago, London and Singapore from their respective websites or other published materials.  As for the average life expectancy, according to the United Nations' statistics released on 1 August 2006, the average life expectancies at birth for males and females in Hong Kong are 79 and 85 years respectively, while those in the US are 75 and 80 years respectively; those in the UK are 76 and 81 years respectively, and those in Singapore are 77 and 81 years respectively.  Information on the average life expectancy on city basis for New York, San Francisco, Washington D.C., Chicago and London is not available.

(b)  As there are many different types of pollutants in the air and the impact of the changes in their concentrations on air pollution is complicated, it is not easy for the general public to understand the air pollution level and its changes from the vast amount of data.  The APIs aim at converting data on different concentrations of major air pollutants into a simple value to make it easier for local population to have a general idea of the air pollution level and its changes. However, since there is at present no uniform method for computing APIs, it is by no means easy to make comparison amongst cities.  For example, the API adopted by Hong Kong is divided into 5 bands with values ranging from 0 to 500.  European cities such as London and Paris both have their indices presented in values between 1 and 10, but the methods of grading and computation in the two places differ.  Although US cities also adopt an index with values ranging from 0 to 500, their computation method is different from that of Hong Kong.  Apart from that, Hong Kong's index, based on real-time computation, is released hourly while some cities, such as Singapore, compute and release their APIs once a day.  Some cities like Tokyo publish only the concentration levels of specific pollutants without establishing APIs.

     In addition, the computation of APIs is based on air quality standards.  However, advanced regions in the world have different ways and requirements for setting their air quality objectives (AQOs).  For example, the EU allows 24 exceedances per year in respect of the limit value for the hourly average of sulphur dioxide, whereas Hong Kong AQO only allows 3 exceedances.  As for RSP, the EU allows 35 exceedances of the daily average limit values per year, while Hong Kong only allows 1 exceedance.  Therefore, we cannot directly compare the AQO of Hong Kong with the air quality standards of other places.  The best way to make such comparison among the cities is to compare the actual concentration of pollutants, which allows us to differentiate the levels directly.  The public will be misled if the standards adopted are substantially different.

Ends/Wednesday, December 20, 2006
Issued at HKT 12:50

NNNN