SINGAPORE - Air quality worsened to nearly unhealthy levels on Friday (Sept 13), marking the start to a weekend that would likely remain hazy, forecasts by the weatherman show.
At 6pm, the 24-hour Pollutant Standards Index (PSI), a measure of air quality here, was 98 in southern Singapore - just shy of the 101 threshold indicating unhealthy air quality.
As of 7am on Saturday, it improved slightly to 92 in the south. The PSI was 84 in the central region, 86 in the north and east, and 91 in the west.
At noon, the PSI went up to 94 in the west, while it it went down to 90 in the south. It was 83 in central and the east, and 88 in the north.
The National Environment Agency (NEA) said on Friday evening that it detected hot spots in both Sumatra and Kalimantan in Indonesia. But based on wind direction, it is smoke haze from Sumatra that has been affecting Singapore.
Said the NEA: "Slightly hazy conditions have been persisting in Singapore today as smoke haze from central and southern Sumatra continues to be blown in by the prevailing winds."
A total of 156 hot spots were detected in Sumatra, mainly in the central and southern parts of the Indonesian island. "Moderate to dense smoke haze continued to emanate from persistent hot spots there, and hazy conditions persisted in Singapore and some parts of peninsular Malaysia," said the NEA.
There were more hot spots in Kalimantan, with a total of 1,043 hot spots detected there on Friday.
NEA said widespread smoke haze was observed over many areas in Kalimantan, with some of the pollution blown over to western Sarawak and the surrounding sea areas.
Weather scientist Koh Tieh Yong from the Singapore University of Social Sciences said hot and dry conditions are likely to continue in South-east Asia in the weeks ahead.
A persistent cold sea surface anomaly off the west coast of Sumatra is discouraging the formation of rainclouds over the region, he said. This could worsen man-made forest fires in Sumatra and Kalimantan.
Added Associate Professor Koh: "Over the past few days, near-surface air turbulence has slowly diffused the haze from the hot spots in Riau and Jambi to our island, compounding the direct transport by winds from hot spots in south Sumatra."
"There is a good chance that hazy days in Singapore will recur in the next few weeks, except when the local rainfall wash out the particulate pollutants."
The NEA said there may be brief showers in Singapore but the weather over Sumatra and Kalimantan is forecast to remain generally dry.