SINGAPORE, Sept 29 — Air quality in all five regions of Singapore entered the unhealthy range on Tuesday morning, with the northern region crossing the threshold at 7am.
CNA reported that the 24-hour Pollutant Standards Index (PSI) in the northern region reached 101 at 7am, while the central region recorded a reading of 155.
The central and southern regions first entered the unhealthy band at 8pm on Monday, when their PSI readings reached 104 and 103 respectively.
The western region followed at 9pm with a reading of 101, while the eastern region moved into the unhealthy range at midnight.
The 24-hour PSI has moved in and out of the unhealthy band in recent weeks, with all five regions last recording unhealthy readings on Sept 15.
The National Environment Agency (NEA) said in a media advisory on Monday evening that the 24-hour PSI was expected to remain between the high end of the moderate range and the mid-unhealthy range over the following 24 hours.
It said moderate to dense smoke haze from fires in southern Sumatra and Kalimantan had drifted towards Singapore.
Although showers are expected in Singapore on Tuesday, the NEA said there was still a risk of smoke haze as prevailing winds were forecast to come from the east or southeast.
The 24-hour PSI, which is based on six pollutants including PM2.5, PM10, ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide, is Singapore’s indicator of daily air quality and forms the basis of the NEA’s health advisories.
A PSI reading between 101 and 200 is classified as unhealthy, while readings of 201 to 300 are considered very unhealthy and those above 300 hazardous.
The one-hour PM2.5 reading measures the hourly average concentration of fine particulate matter measuring 2.5 micrometres or smaller, which is the dominant pollutant during haze episodes, and differs from the 24-hour PSI, which reflects air quality averaged over the preceding 24 hours.
