The table shows that for each of the pollutants NO2, TSP and RSP there is a clear pattern of non-compliant monitoring locations from 1994 to 1997, although there were fewer non-compliances in 1998 than previous years. For nitrogen dioxide, the daily AQO was exceeded between 1994 and 1997 at Mong Kok and the severity of the non-compliance (the percentage of the AQO for the highest exceedence) increased over this period, reversing a trend of improvements in NO2 levels during the late 1980s. The annual AQO for TSP has been regularly breached at Kwun Tong, Sham Shui Po, Central/Western and Mong Kok, with the greatest exceedences all recorded at Mong Kok. The same locations have shown non-compliances with the annual AQO for RSP (except for Central/Western which was compliant in 1996), although the pattern changed in 1998 where a non-compliance was picked up at the new roadside station in Causeway Bay.

There were no continuous AQO exceedences for sulphur dioxide between 1993 and 1998. Although a number of exceedences of the 24 hour AQO were recorded in the late 1980s, from 1990 onwards, following regulations to limit sulphur content in solid and liquid fuel oil(), there have been no further exceedences of the 24 hour AQO (and the last one hour exceedence was in 1994). SO2 levels have also fallen due to the decline in the number of major industrial sources of pollution (eg incinerators at Kwai Chung and Kennedy Town). The principal remaining sources of this pollutant are from the coal-fired power stations at Lamma Island and Castle Peak, both of which have been fitted with pollution abatement equipment.

In order to determine trends in longer term levels of air pollution in Hong Kong, data are presented in Annex G2 for annual average concentrations of the pollutants monitored at each station and for the territory overall. Long term trends in both roadside and ambient levels for six major pollutants (SO2, NO2, TSP, RSP, CO and O3) are also shown graphically in Figures 5.4b-d, Figures 5.4e-g (sourced from EDP 1998d) with respect to their relevant annual air quality objective. These data show increasing trends in the Hong Kong annual average (ambient) concentrations for NO2, though SO2 levels continue to decline at ambient (urban and new town stations). Ambient levels of particulates (both TSP and RSP) have remained consistently high over the last 10 years with both pollutants close to their respective permissible AQO limits. Whilst annual average concentrations of ozone have only risen slightly, there were two exceedences of the hourly AQO in 1996 and the highest level recorded in 1998 (at Tap Mun) of 239 ug m-3 was just slightly lower than the hourly AQO of 240ugm-3. Although the results for ozone since 1996 have been greatly affected by the inclusion of data from additional monitoring stations, rising levels of this pollutant (along with NO2) are a cause for increasing concern over the formation of photochemical smog, although additional data is required to establish the long term trend of the background ozone level.