Air quality in unhealthy range across most of Singapore

SINGAPORE: Air quality in four of Singapore’s five regions remained in the unhealthy range on Tuesday (Oct 6) morning, while the south improved to the moderate range after all regions recorded unhealthy readings on Monday.

As of 6am, the 24-hour Pollutant Standards Index (PSI) readings were 130 in central Singapore, 117 in the west, 112 in the east and 107 in the north.

The 24-hour PSI reading in southern Singapore was 95, within the moderate range.

The 1-hour PM2.5 readings, which give a more current indication of air quality, were in the elevated band in central, western and eastern Singapore at 6am.

For immediate outdoor activities, people should refer to the 1-hour PM2.5 readings and corresponding personal guide, the National Environment Agency (NEA) said. 

The 24-hour PSI forecast and health advisories should be used when planning outdoor activities for the next 24 hours.

When 1-hour PM2.5 levels are elevated, healthy people are advised to reduce strenuous outdoor activity for the next hour, while the elderly, pregnant women, children and people with chronic heart or lung conditions should avoid such activity.

In an update on Monday evening, NEA said moderate to dense smoke plumes in the southern parts of Sumatra were observed drifting into Singapore, while smoke haze was also observed in parts of Kalimantan.

Dry conditions are expected to persist over southern Sumatra and Kalimantan. With prevailing winds expected to blow from the southeast or east-southeast, smoke haze could continue to drift towards Singapore, NEA said.

The 24-hour PSI for Singapore was forecast to be in the high moderate to mid unhealthy range, NEA said.

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".