SINGAPORE — The haze in Singapore took a turn for the worse tonight (Oct 19), with both one-hour PM2.5 and three-hour Pollutant Standards Index (PSI) readings shooting up. At 11pm, the one-hour PM2.5 concentration reached 471 µg/m3 in the west region, the highest recorded so far for this year.

The one-hour PM2.5, which is fine particulate matter, rocketed from 35 to 164 microgrammes per cubic metre (µg/m3) at 9pm, to 55 to 442 µg/m3 at 10pm. The worst-hit was western Singapore, followed by the southern areas. 

At 11pm, the one-hour PM2.5 was 35 - 471µg/m3, with the western Singapore at 471µg/m3, southern Singapore at 301µg/m3 and central Singapore at 138µg/m3. 

The NEA in an update said that the sharp deterioration in haze conditions in several regions of Singapore, from about 9pm, was due to denser haze from the sea areas south of Singapore being blown in by the prevailing south-southeasterly winds. "The current haze conditions are expected to gradually improve over the next few hours," said the NEA.

The NEA said on its website that the 1-hour PM2.5 concentrations reflect the PM2.5 levels averaged over one hour, and can give an indication of the current air quality. However, the one -hour PM2.5 concentration levels can be volatile and tend to fluctuate over the day especially during periods of transboundary haze. Short-term fluctuations will also be very heavily influenced by weather conditions.

The three-hour PSI, meanwhile, also surged to 152 at 10pm from 96 as at 9pm. At 11pm, the three-hour PSI breached the 200-mark, at 209. The 24-hour PSI at 11pm was 104-152, which is in the unhealthy range.

Earlier in the day, a shift in the prevailing winds brought about an improvement in the haze situation.

The National Environment Agency (NEA), in its evening update, said hazy conditions can still be expected tomorrow, with the 24-hour PSI expected to be in the low to mid section of the unhealthy range. Reduced visibility is also expected if PM2.5 concentration levels are elevated, said the NEA.

A total of 233 hotspots were detected in Sumatra today. Moderate to dense smoke haze is still persisting in parts of central and southern Sumatra, and some haze from Kalimantan is also observed to have spread to the sea areas southeast of Singapore, said the NEA.

Given the air quality forecast for the next 24 hours, the NEA advised healthy persons to reduce prolonged or strenuous outdoor physical exertion. The elderly, pregnant women and children should minimise prolonged or strenuous outdoor physical exertion, while those with chronic lung or heart disease should avoid prolonged or strenuous outdoor physical exertion. Persons who are not feeling well, especially the elderly and children, and those with chronic heart or lung conditions, should seek medical attention.