SINGAPORE - There may be occasional haze on Tuesday, said the National Environment Agency (NEA) in its daily haze advisory.

The 24-hour Pollutant Standards Index (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. At 7pm on Monday, the PSI was 92-108.

The hazy conditions in Singapore have been gradually improving on 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, but dropped to 70 at 7pm.

NEA said in an earlier advisory on Monday afternoon that the haze condition was due to smoke haze from southern Sumatra in Indonesia, blown in by the prevailing southerly winds. It detected 382 hotspots in southern Sumatra 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 Monday, healthy people should reduce prolonged or strenuous outdoor physical exertion, the NEA said in its haze advisory on Sunday. 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, when the three-hour PSI soared from 86 in the afternoon to hit 127 at 9pm.

This was after several days of clear air as the south-west monsoon season comes to an end, which was followed by an inter-monsoon season typically lasting from October to November. The inter-monsoon season is characterised by more rainfall as well as light and variable winds.