SINGAPORE - The likelihood of haze affecting the Republic remains low for the next 24 hours despite a sharp rise in the number of hot spots detected in Sumatra, the National Environment Agency said on Tuesday evening (Oct 1).

It noted that weather over southern Sumatra was dry, with 563 hot spots detected on Tuesday, a sharp increase from the 90 reported on Monday. Most of the hot spots were located in the southern provinces of South Sumatra and Lampung.

Still, showers expected in Singapore and Sumatra over the next few days mean the haze is unlikely here.

For the next 24 hours, NEA said 24-hour Pollutant Standards Index (PSI) readings are expected to be in the moderate range, while one-hour PM2.5 concentration readings, which are a better measure of current air quality, should be in the normal band.

A PSI reading of zero to 50 indicates good air quality, while a reading of 51 to 100 is in the moderate range. A reading of 101 to 200 is considered unhealthy, very unhealthy from 201 to 300, and hazardous when the reading is more than 300.

The PM2.5 concentration scale has four bands: 0 to 55 for normal, 56 to 150 for elevated, 151 to 250 for high, and very high for any higher readings.

At 6pm on Tuesday, 24-hour PSI readings were 57-64 in the moderate range. The PM2.5 concentration readings were 11-31 micrograms per cubic m, in the normal band.

NEA said that there were showers over parts of Singapore and in northern and central Sumatra on Tuesday.

The environment agency has said that the health impact of the haze is dependent on one's health status, the PSI level and the length and intensity of outdoor activity.

Doctors The Straits Times has spoken to have warned that vulnerable groups, such as patients with pre-existing medical conditions, could experience increased discomfort on poor air quality days.