SINGAPORE - Air quality in Singapore continues to improve on Tuesday, with the three-hour Pollutant Standards Index (PSI) falling further in the moderate range to 69 at 2pm.

The 24-hour PSI is also in the moderate range of 74 to 81, with the haze over Singapore showing signs of easing since Monday afternoon.

The National Environment Agency said in an advisory on Monday evening that occasional haze is expected on Tuesday and that the 24-hour PSI is expected to be in the high-end of the moderate range (51-100), and may enter the low end of the unhealthy range (101- 200), should the winds turn unfavourable.

The hazy conditions in Singapore have been gradually improving since Monday afternoon due to a change in the prevailing wind direction, blowing from the south-east. The three-hour PSI peaked at 116 at 10am on Monday, but dropped to 70 by 7pm.

The haze was due to smoke haze from southern Sumatra in Indonesia, blown in by the prevailing southerly winds. A total of 382 hotspots in southern Sumatra were detected on Monday.

The health impact of haze is dependent on one's health status, the PSI level, and the length and intensity of outdoor activity. Reducing outdoor activities and physical exertion can help limit the ill effects from haze exposure, the NEA said.

Given the air quality forecast for Tuesday, healthy people should reduce prolonged or strenuous outdoor physical exertion. This is especially so for the elderly, pregnant women and children.

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.

The haze had returned on Sunday, after several days of clear skies. The three-hour PSI soared from 86 on Sunday afternoon to hit 127 at 9pm that day.