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SINGAPORE \u2013 The air quality in Singapore hovered between the moderate and unhealthy bands overnight into the morning of Oct 21 after dipping earlier in the evening.<\/p>\n
At 7am on Oct 21, the 24-hour Pollutant Standards Index (PSI) stood in the unhealthy range at 133 in the west and 116 in the central region while the rest of the island saw figures in the moderate range: north (82), south (91) and east (97).<\/p>\n
This comes after the 24-hour PSI readings registered unhealthy readings in four out of the five regions \u2013 south, east, west and central \u2013 for most of the evening on Oct 20.<\/p>\n
Air quality is considered moderate when the PSI \u2013 a 24-hour rolling average of six key air pollutants \u2013 is in the range of 51 to 100, and unhealthy when it is in the range of 101 to 200. Beyond 200, it enters the very unhealthy band.<\/p>\n
The highest 24-hour PSI reading this haze season was recorded at 10am on Oct 18, where it hit 230 in the western region, putting air quality in the very unhealthy range.<\/p>\n
Meanwhile, the one-hour PM2.5 readings ranged from 35 to 81 at 7am with the western and central regions registering values in the elevated band at 81 and 59 respectively.<\/p>\n
The hourly PM2.5 readings are measured in micrograms per cubic metre and are a gauge of the current air quality.<\/p>\n