Rare 'normal' PM2.5 in 3 regions on Oct 18; PSI at season-high 230 in western Singapore
No, this photo of Punggol isn't one taken on better days. Clear skies and good air quality have been in short supply since Oct 5, when Singapore started recording 24-hour Pollutant Standards Index (PSI) readings in the unhealthy range. Singapore calculates its PSI based on six pollutant particulate matter — PM10 and PM2.5, sulphur dioxide, nitrogen dioxide, ozone and carbon monoxide.With one-hour PM2.5 concentration readings in the high and very high bands over the past two weeks, PSI readings have consequentially reached the very unhealthy range, including the season-high of 230 in western Singapore at 10am and 11am on Sunday (Oct 18).The one-hour PM2.5 reading reflects current air quality conditions, making it a useful indicator when planning immediate outdoor activities.Advisories on immediate outdoor activities are also given based on the varying concentration readings. At 11am on Sunday, PM2.5 was in the normal band (0 to 55µg/m3) in northern, eastern and southern Singapore.In this condition, all persons, including those who are vulnerable, may continue with normal activities.