SINGAPORE – The hazy conditions in recent days in Singapore are expected to ease when the winds strengthen as the number of hot spots in the surrounding region has remained low, said the National Environment Agency (NEA).
“Singapore is not expected to experience transboundary haze in the coming week as the number of hot spots detected by satellites remains low, and no significant haze has been observed in the surrounding region.
“However, localised hazy conditions can sometimes occur during the night and early morning due to an accumulation of particulate matter under light wind conditions,” said NEA.
In the past five days up until Friday at 5pm, the 24-hour Pollutant Standards Index (PSI) reading was good to moderate, ranging from 18 to 74.
NEA noted that average hourly PM2.5 levels were 18 micrograms per cubic m – slightly higher than the previous week’s 11 micrograms per cubic m. Still, the levels are within NEA’s guideline for the public to continue with normal activities.
PM2.5 refers to fine particles – usually airborne – which are 2.5 microns or smaller and can be lodged deep in the lungs, posing severe health risks. For comparison, a strand of human hair is about 70 microns thick.
Air quality scientist Erik Velasco told The Straits Times that Singapore’s higher PM2.5 levels correspond with those of the surrounding region. Levels of PM2.5 have been a predominant pollutant during periods of transboundary haze.
“We must pay attention to fires sparking in Indonesia’s islands. Those are the fires that trigger the worst smoke-haze episodes in Singapore,” he said.
“Satellites often fail to detect hot spots in South-east Asia because of cloudiness. It could also be because the few hot spots detected correspond to fairly widespread and intense fires.”
Associate Professor Koh Tieh Yong, a weather and climate scientist at the Singapore University of Social Sciences (SUSS), has observed a dip in air quality in the south of Singapore, which is closest to the few hot spots in Riau, Jambi and South Sumatra.
“Singapore is in the inter-monsoon season and experiences light variable winds,” he said. “When a sea breeze blows onshore from the south, areas in the south-west, south, south-east and east regions of Singapore will ‘sample’ the mentioned poorer-quality air.”
While not many hot spots have been seen in Indonesia and Malaysia, Dr Velasco said global air quality forecasting systems have been reporting higher levels of PM2.5 in Riau and the Malaysian peninsula as recent dry conditions have sparked fires in Sumatra, Kalimantan and Malaysia.
On why Singapore recently experienced hazy mornings before conditions cleared up in the evenings, Prof Koh explained that this was due to the temperature dropping at night while relative humidity increases, raising the pollutant concentration.
“When the sun rises, these particles scatter the low-angled light rays and create the orange, hazy look in the morning. But as the day warms up, some condensed particles evaporate, while sunlight intensity also climbs, clearing up the air.”
