UPDATE (Monday Sept 7)
SINGAPORE - The 24-hour Pollutant Standards Index (PSI) readings for the nation were in the 91-106 region for much of yesterday (Sunday Sept 6) afternoon from 4pm, right up till 12am this morning. The readings for the western part of Singapore were consistently above the 101 mark while the readings for the rest of Singapore mainly stayed in the 90s.
Air quality is considered to be in the "unhealthy" range when the PSI is in the 101 to 200 mark. Air quality is considered to be "moderate" when the PSI is between 51 and 100.
The National Environment Agency (NEA) advises people to reduce outdoor physical exertion when the PSI is in the unhealthy range, especially for the elderlies and children, and pregnant women.
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A previous version of this report erroneously said that the 3-hour PSI was in the unhealthy range. NEA has written to clarify that air quality is "unhealthy" only when the 24-hour PSI ranges from 101-200. "During transboundary haze episodes, the 3-hour PSI reflects the PM2.5 concentration levels averaged across 3 hours and is only an indicative measure which is not tied to MOH's health advisory," it said in an e-mail message on Monday. We apologise for the error.