The air quality in Singapore took a sharp turn for the worse yesterday, and may remain so for the next few days.
For the first time in three years, the 24-hour Pollutant Standards Index (PSI) - a measure of air quality - crossed the "unhealthy" range and continued to climb into the night. At 11pm, the PSI reading was 114. The unhealthy range is from 101 to 200.
The worsening haze led to stocks of face masks running out at some stores, Singaporeans cancelling their outdoor plans and tourists rueing that the bad weather had put a dampener on their sightseeing activities.
The National Environment Agency (NEA) said the deteriorating air quality is due to winds blowing more smoke haze from Sumatra, which is south of Singapore. For the next few days, dry weather can be expected in Singapore and over central and southern Sumatra, and the NEA warned that the PSI may enter the mid-section of the unhealthy range if denser haze is blown in.
Analyst Jeslyn Lerh, who lives in the west, shelved her plans to get some exercise at Bukit Timah Hill yesterday.
The 26-year-old said: "The haze foiled my plans to go trekking today. The smoke is infiltrating my apartment and we are turning on extra fans just to disperse it."
As some stores reported that they had sold out of N95 masks, the Health Ministry said there are sufficient stocks in the warehouses and government stockpiles, and that it is working with retailers to restock their shelves.
Dr Jim Teo, 45, a respiratory physician from Parkway East Hospital, told The Sunday Times that he has seen about a 10 per cent increase in the number of patients seeking his advice on the deteriorating air quality. He said these patients were usually people who are more vulnerable to changes in air quality, such as those with asthma or sensitive nasal tracts.
The PSI last hit the unhealthy range in August 2016, when it peaked at 143 in the west.
Yesterday, a training session for The Straits Times Run in Punggol was called off, as was an international women's cycling event.
At Jurong Bird Park, Taiwanese visitor Wu Yuming, 26, said her family was seeking refuge in the park's air-conditioned dining facilities after "feeling like (they) breathed in smoke for over an hour" during their visit.
The NEA advises that people reduce prolonged or strenuous outdoor activities when the PSI enters the unhealthy range.
Children, elderly people and pregnant women should minimise such activities while those with chronic lung or heart diseases should avoid them entirely, the NEA said.
For the last two weeks, Indonesia and parts of Malaysia have been choked by haze from raging forest fires in Sumatra and Kalimantan in Indonesia, as well as hot spots in parts of Malaysia.
According to NEA, 450 hot spots were detected, mostly in the Riau, Jambi and South Sumatra provinces, yesterday, a sharp increase from the 156 detected the day before.
Singapore had until now been spared the haze by favourable wind directions. The haze comes just one week before the Formula One race in the Marina Bay area, which is scheduled from Friday to Sunday.
In a Facebook post yesterday, Minister for the Environment and Water Resources Masagos Zulkifli said Singapore has offered technical firefighting assistance to Indonesia.
Singapore's worst encounter with the haze lasted for several weeks in 2015, when the PSI crossed the hazardous level of over 300, forcing schools to close.