Haze watch Oct 17: Hourly PM2.5 in western region back in high band, PSI remains unhealthy
After 18 hours in the elevated band, hourly PM2.5 in western Singapore climbed back into the high band (151 to 250µg/m3) at 11am on Saturday (Oct 17) morning.The western concentration reading returned to the elevated band (56 to 150µg/m3) at 5pm on Friday and was gradually easing into the lower-half of the said band.But at 11am, one-hour PM2.5 soared from 111 to 158µg/m3.Meanwhile, the 24-hour Pollutant Standards Index (PSI) is in the unhealthy range across Singapore, with the highest reading of 184 in the central region, followed by 176 in western Singapore.PSI vs PM2.5 While members of the public can use the PSI forecast to plan activities, they should track the latest hourly PM2.5 concentration readings before taking part in outdoor activities.Although a low 24-hour PSI may generally indicate a good condition, a high one-hour PM2.5 reading could indicate that conditions have recently worsened, even though the longer-term average has not risen yet.