Singapore air quality improves to moderate range after unhealthy readings

SINGAPORE: Air quality across Singapore improved to the moderate range on Saturday (Sep 5), after three regions recorded unhealthy 24-hour Pollutant Standards Index (PSI) readings earlier in the day.As of 10pm, the central region recorded a 24-hour PSI of 96, down from a peak of 123 at 1am, according to the National Environment Agency (NEA).The west and east regions also returned to the moderate range, recording PSI readings of 89 and 79 respectively at 10pm.Earlier in the day, both regions had entered the unhealthy range, with the west recording a PSI of 103 and the east 102 at 6am. The north and south regions remained in the moderate range throughout the day, with a PSI of 76 and 75 respectively as of 10pm. The 24-hour PSI entered the unhealthy band of 101 to 200 at 7am on Friday, marking the first time the PSI had exceeded 100 since Oct 8, 2023.This prompted the NEA on Friday to start issuing daily haze advisories, including a 24-hour PSI forecast, to help the public plan activities and events for the following day.Singapore could continue to experience transboundary haze if fires in Indonesia remain active, with the 24-hour PSI forecast to be at the higher end of the moderate to the lower end of the unhealthy range, NEA said in Saturday's daily advisory. It noted that most parts of the surrounding region remained dry on Saturday, with moderate to dense smoke plumes over the southern and central parts of Sumatra and various parts of Kalimantan continuing to drift towards Singapore. Dry conditions are expected to persist over Singapore and the surrounding region in the coming days, with prevailing winds blowing from the southeast or south, NEA added.The 24-hour PSI is Singapore's indicator of daily air quality and forms the basis of NEA's daily health advisories. It is calculated using six air pollutants - PM2.5, PM10, ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide. The one-hour PM2.5 reading measures the hourly average concentration of fine particulate matter (PM2.5), the dominant pollutant during haze episodes.While the 24-hour PSI is an average of the past 24 hours, the one-hour PM2.5 reading reflects the air quality at a single point in time.A 24-hour PSI reading is considered "very unhealthy" when it is within the 201-300 range, and "hazardous" when it goes over 300.In an earlier joint media release issued on behalf of agencies in the Haze Task Force, NEA said those in the task force have implemented their respective action plans and advisories to protect public health and well-being.NEA's daily haze advisories will include the 24-hour PSI forecast, which can be used by the public to plan their activities and events for the next 24 hours.