Air quality in unhealthy range across most of Singapore

On Tuesday morning, Singapore's air quality remained predominantly unhealthy, according to the National Environment Agency (NEA). Four of the five regions reported PSI readings of 130, 117, 112, and 107, placing them in the high moderate to mid unhealthy range. Only the south's PSI reading of 95 was within the moderate range. The 1-hour PM2.5 readings, indicating more immediate air quality conditions, were elevated in central, western, and eastern Singapore at 6am.

For those engaging in outdoor activities, the NEA advises referring to the 1-hour PM2.5 readings and personal guidelines. When 1-hour PM2.5 levels are elevated, healthy individuals should limit strenuous outdoor activities for the next hour, while the elderly, pregnant women, children, and those with chronic heart or lung conditions should avoid such activities.

Smoke plumes from southern Sumatra and parts of Kalimantan were observed drifting into Singapore, with dry conditions expected to persist over the regions. Prevailing southeast or east-southeast winds could continue to transport smoke haze towards Singapore. The 24-hour PSI, which averages air quality over the past 24 hours, is Singapore's primary indicator for daily air quality and determines the issuance of NEA's health advisories.

It is derived from six pollutants: PM2.5, PM10, ozone, sulphur dioxide, nitrogen dioxide, and carbon monoxide. The 24-hour PSI reading indicates unhealthy air quality when it falls between 101 and 200, very unhealthy between 201-300, and hazardous above 300. A 1-hour PM2.5 reading classifies air quality into four bands: normal, elevated, high, and very high.

Elevated levels range from 56 to 150, high levels between 151 and 250, and very high levels above 250.