At 3pm, the 24-hour PSI readings ranged from 96 to 119. SINGAPORE: Air quality remained unhealthy in three regions of Singapore on Sunday (Oct 25), while the 24-hour Pollutant Standards Index (PSI) readings in the other two dropped into the good. Singapore’s haze situation remained a concern on Sunday (Oct 25), with three regions recording unhealthy air quality despite hourly PM2.5 readings remaining within the normal range nationwide.