SINGAPORE, Sept. 29 -- Air quality in all five regions of Singapore entered the unhealthy range on Tuesday morning, with the northern region crossing the threshold at 7am.

CNA reported that the 24-hour Pollutant Standards Index (PSI) in the northern region reached 101 at 7am, while the central region recorded a reading of 155.

The central and southern regions first entered the unhealthy band at 8pm on Monday, when their PSI readings reached 104 and 103 respectively.

The western region followed at 9pm with a reading of 101, while the eastern region moved into the unhealthy range at midnight.

The 24-hour PSI has moved in and out of the unhealthy band in recent weeks, with all five regions last recording unhealthy readings on Sept 15.

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