SINGAPORE - Residents of Singapore woke up to a slightly clearer sky and better air this morning as the haze cleared a little overnight.

As at 9am today (Sept 4), The 24-hour Pollutant Standards Index (PSI) stood at 80-90, in the moderate range of under 100, according to the National Environment Agency (NEA) website. Three-hour PSI was at 73.

At 11am yesterday (Sept 3), the three-hour PSI hit 107, the lower end of the unhealthy range, while the 24-hour PSI was in the high moderate range of 83-96 at 11pm yesterday.

Both readings have been falling steadily overnight.

The three-hour PSI reflects the PM2.5 concentration levels averaged across three hours and is an indicative measure that is not tied to the Health Ministry's health advisory.

The NEA said in its forecast yesterday that occasional hazy conditions can still be expected today. Thundery showers are forecast in the late morning and early afternoon.

The haziness is due to the spread of smoke haze from Sumatra, Indonesia, under weakening wind conditions over Singapore, the agency said.

Given the air quality forecast, healthy people should reduce prolonged or strenuous outdoor physical exertion, the NEA said. The elderly, pregnant women and children should minimise prolonged or strenuous outdoor physical exertion, while those with chronic lung or heart disease should avoid prolonged or strenuous outdoor physical exertion.

Those who are not feeling well, especially the elderly and children, and those with chronic heart or lung conditions, should seek medical attention.