SINGAPORE - Singapore's air pollution level rose to "hazardous" levels late on Wednesday, with the three-hour pollution index hitting the highest on record, as smoke from Indonesian forest fires enveloped the city-state.
The three-hour Pollution Standards Index (PSI) soared to 321 at 10pm local time (1300 GMT), up from 190 just two hours earlier.
However, the PSI level eased slightly down to 282 at 11pm - the last three-hour PSI reading for the day. This still puts it within the "very unhealthy" range and dangerously close to "hazardous" levels.
A PSI reading above 300 indicates "hazardous" air quality and 201-300 means "very unhealthy".
The 321 level is also above the previous 226 record reached in Singapore in 1997 when smog from Indonesian forest fires disrupted shipping and air travel across Southeast Asia. It caused widespread health problems and cost the regional economy billions of dollars as a result of business and air transport disruptions.
The illegal burning of forests to clear land for palm oil plantations is a recurring problem in Indonesia, particularly during the annual dry season from June to September.
PSI levels climbed steadily throughout the day, starting from 77 at 6am to 103 at 11am. It reached 170 at 2pm, before hitting 190 at 8pm.
The 24-hour 4pm PSI reading ranged from 101 to 121, with the highest PSI readings in the North and West. The PSI reading of PM2.5 concentration, or very fine particulate matter, was between 112 to 143 micrograms per cubic metre.
Around 30 times smaller than a human hair, PM2.5 particles have long been identified as a respiratory problem, as their size enables them to lodge deep in the lungs and penetrate the bloodstream.
As these very fine particles are more hazardous to the health, a range of 40 to 65 typically carries a health advisory from the National Environment Agency (NEA).
Given the current hazy conditions, NEA has advised children, the elderly and those with heart or lung diseases to reduce prolonged or heavy outdoor activities.
The general population should avoid unnecessary outdoor activity.
The haze situation could worsen in the coming days, as the number of hot spots in Sumatra quadrupled from 46 to 187 within just a week.
According to the National Environmental Agency, June to September is the traditional dry season for the southern ASEAN region. The agency observed that weather conditions in the region have become drier.
In the coming months, occasional extended periods of drier weather can be expected in the region and transboundary smoke haze could affect the region during periods of persistent dry weather conditions, NEA said.