In accordance with the review findings as endorsed by the Working Group and supported by the Advisory Council on the Environment (ACE), it is recommended to further tighten the AQOs for sulphur dioxide (SO2) and fine suspended particulates (FSP/PM2.5), as follows:
The 24-hour AQO for SO2 could be tightened from WHO IT-1 level (125μg/m3) to IT2 level (50μg/m3) with the current number of exceedance allowed (three) remains unchanged;
Fine Suspended Particulates PM2.5
The annual AQO for PM2.5 could be tightened from IT-1 level (35μg/m3) to IT-2 level (25μg/m3);
The 24-hour AQO for PM2.5 could be tightened from IT-1 level (75μg/m3) to IT-2 level (50μg/m3) with the number of exceedances allowed increased from the current 9 to 35.