The one-hour PM2.5 reading hit 442 for the west of Singapore at 10pm yesterday.
Elsewhere during the hour, readings ranged from 51 to 299, with the southern and central parts of Singapore recording 299 and 130 respectively. PM2.5 refers to particles that are 2.5 microns or smaller. The 24-hour Pollutant Standards Index (PSI) stood at 101-136 in the unhealthy range, while the three-hour PSI was 152 as of 10pm.
The National Environment Agency said hazy conditions are likely to persist in the next 24 hours, with the 24-hour PSI expected to be in the low- to mid-section of the unhealthy range.
Meanwhile, the Singapore team sent to Indonesia to help tackle the haze-causing fires has performed 47 water-bombing operations and put out about 35 hot spots in Indonesia since it joined multinational efforts to douse the fires raging there.
In a Facebook post yesterday, Defence Minister Ng Eng Hen said it has been a team effort for the 40 personnel from the Singapore Armed Forces (SAF) and Singapore Civil Defence Force (SCDF) who arrived more than a week ago in Palembang.
Dr Ng said: "They know the task is difficult and that it is hard to put out fires without the help of rain. But the SAF's presence as part of a multinational effort does send a strong signal that there is international attention and support as Indonesia seeks to address the problem of transboundary haze which has affected many neighbouring countries."
He said one of the team members is a full-time national serviceman who volunteered for the mission.
On Oct 10, the SAF sent a 34-strong team to Indonesia, accompanied by a six- man Disaster Assistance and Rescue Team from the SCDF. Also deployed was a CH-47D Chinook helicopter and two C-130 planes.
Australia and Malaysia are also helping in the firefighting efforts.
Correction note: An earlier version of the article stated that the one-hour PM2.5 reading of 442 was believed to be the highest this year. The National Environment Agency said the PM2.5 reading of 471 micrograms per cubic m in the west region at 11pm on Oct 19 was the highest recorded so far this year.