Haze in Singapore: PM2.5 readings fluctuate between ‘normal’ and ‘elevated’ bands

SINGAPORE – Haze conditions islandwide improved on Oct 19 from a day earlier, even as hourly PM2.5 levels fluctuated between the normal and elevated bands throughout the day.

At 10pm, the PM2.5 readings were in the normal range in the north (43) and east (46), while those in the west (89), central (77) and south (62) were elevated.

Islandwide PM2.5 readings were normal from noon to 2pm – the first time since Oct 4 – before spiking into the elevated band in some regions later in the afternoon.

Readings across the country ranged from 22 to 94 from midnight through 10pm on Oct 19, down from the 26 to 201 range recorded the day before.

The hourly PM2.5 readings are measured in micrograms per cubic metre and are a gauge of the current air quality.

Scores from zero to 55 represent normal values, those between 56 and 150 indicate an elevated concentration of fine particles, while readings between 151 and 250 are considered high and scores above 251 are classified as very high.

The highest PM2.5 reading this haze season was recorded at 3pm on Oct 14 in the western part of the island at 288.

Meanwhile, the 24-hour Pollutant Standards Index (PSI) readings are also falling across the board, although pollution levels in two of the five regions were still classified in the “unhealthy” band.

At 10pm, PSI readings stood at 87 in the north, 90 in the south and 92 in the east – all in the moderate range – while readings in the west (114) and the central regions (109) remained in the unhealthy band.

On Oct 18, four out of five regions in Singapore recorded unhealthy PSI levels, while the west remained in the “very unhealthy” band for most of the day after hitting a season high of 230 at 10am.

Air quality is considered moderate when the PSI – a 24-hour rolling average of six key air pollutants – is in the range of 51 to 100, and unhealthy when it is in the range of 101 to 200. Beyond 200, it enters the very unhealthy band.

Moderate to unhealthy air quality on Oct 20

The National Environment Agency (NEA) forecasts moderate to unhealthy air quality for Oct 20, with PSI levels expected to range from 90 to 160.

The agency said shifting winds, which blew from the south-south-east, and nearby rainfall helped to clear the air on Oct 19.

Nonetheless, smoke haze from Kalimantan and Sumatra in Indonesia was still observed near Singapore.

Showers are expected over Singapore and the surrounding region on Oct 20, NEA said, adding that south-south-easterly winds may reduce smoke haze blowing from Kalimantan to Singapore.

However, some smoke haze from Sumatra may drift towards Singapore, it said.

Air quality may deteriorate in the coming days.

From the night of Oct 19 to Oct 22, the winds are likely to turn east-south-easterly, with dry conditions forecast over the surrounding region, including parts of Kalimantan, said NEA.

This may bring smoke haze from fires in Kalimantan towards Singapore.

The Republic is currently experiencing its 15th day of unhealthy air – surpassing the 14-day stretch during the 2015 haze crisis, during which bad air persisted for from Sept 23 to Oct 7.