MaIn the absence of the scientific information necessary to quantitatively apply the assimilative capacity concept as a water quality management tool (for marine and freshwaters alike), it will be necessary to continue to adopt a management approach based on in situ monitoring to assess trends in ambient conditions. This approach, though retrospective in nature, if applied consistently (ie ensuring long-term continuity of data sets) and comprehensively throughout Hong Kong waters, will provide a basis for swift identification of adverse impacts and prompt remedial action. Such actions will also help to offset increasing wastewater treatment costs (currently effectively subsidised by Government) which would otherwise arise as assimilative capacity is denuded and ever greater quantities and standards of treatment become necessary. The powers of the regulators to act promptly need to be strengthened via suitable institutional mechanisms.

Assimilative Capacity of Air (including Noise) - Issues and Trends

• In 1998, a number of non-compliances were recorded for the Air Quality Objectives (AQOs) for Total Suspended Particulates (TSPs), Respirable Suspended Particulates (RSPs) and Nitrogen Dioxide (NO2). There is also a clear pattern of monitoring stations at which non-compliances for these pollutants have been recorded between 1993 and 1998.

• Longer term trends in air pollutants measured by EPD show increases in annual average concentrations of NO2, decreases in SO2, and consistently high levels of particulates with both TSPs and RSPs being close to their respective AQO limits. Rising levels of ozone, which is a contributor to incidences of photochemical smog, is also of concern for air quality.

• Poor air quality at many roadside locations has been attributed to vehicle emissions, and levels of NO2 and RSPs are particularly high in the urban areas of Hong Kong Island and Kowloon. Much of the particulate pollution in these locations can be attributed to the large stock of diesel vehicles on Hong Kong's roads.

• Declining air quality in Hong Kong is an issue of serious concern and it is likely that a range of technical and policy measures (including demand management) will be required to limit emissions from static and mobile sources. Fuel use, energy efficiency, demand side management and measures to encourage public transport (potentially including road pricing) will all need to be considered to address the problem, particularly in the light of recent studies linking air pollution to greater incidences of respiratory disease in people.

• Levels of toxic air pollutants measured since 1997 in Hong Kong are difficult to interpret for trends but levels monitored to date appear to be well within international health guidelines.

• Despite recent reductions in annual greenhouse gases in Hong Kong, projections undertaken in a recent study for EPD (yet to be officially endorsed) suggest that emissions are likely to increase more rapidly between 2000 and 2010 than during the previous decade, principally as a result of projected increases in energy consumption.

• Noise in Hong Kong is a prominent environmental issue and it is estimated by EPD that around 1 million people in the SAR are exposed to excessive noise, principally as a result of road traffic sources. Despite planning measures and improvements in building design and insulation, pedestrians and others working and living close to major urban roads will continue to be exposed to high levels of noise in future.