Air quality in central Singapore crossed into the unhealthy range at 11am on Saturday (Oct 3) morning, while readings in the other four regions remained moderate.
At 1pm, the 24-hour Pollutant Standards Index (PSI) in the central region rose to 105. Readings were 96 in the east, 93 in the west, 87 in the south and 77 in the north.The 1-hour PM2.5 reading at 1pm, which reflects air quality at a single point in time, was in the elevated band in the central region.
The latest readings come after the National Environment Agency (NEA) said in an advisory on Friday evening that smoke haze could be transported towards Singapore under prevailing southeasterly or southerly winds.
Moderate to dense smoke plumes from southern Sumatra had been observed drifting towards Singapore, while smoke haze was also observed from fires in Kalimantan, NEA said.
Dry conditions were expected to persist over Singapore and the surrounding region on Saturday, with NEA forecasting the 24-hour PSI for Singapore to be in the moderate to low-unhealthy range.
The 24-hour PSI is Singapore’s indicator of daily air quality and forms the basis of NEA’s daily health advisories. It is calculated using six air pollutants – PM2.5, PM10, ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide – and reflects the average air quality of the past 24 hours.
The 1-hour PM2.5 reading, on the other hand, is the hourly average of the PM2.5 pollutant levels. PM2.5 is fine particulate matter with a diameter of 2.5 micrometres or shorter, and is the dominant pollutant during haze that causes harm to health.
A 24-hour PSI reading is considered “unhealthy” when it is in the 101 to 200 range, “very unhealthy” when it is within the 201-300 range, and “hazardous” when it goes over 300.
The hourly PM2.5 reading is classified in four bands: normal, elevated, high and very high. It is considered elevated when it ranges from 56 to 150. The “high” band ranges from 151 to 250, and readings above that are classified as “very high”.
CNA
