PSI stands for 'Pollutant Standards Index'. It is an index of daily air quality levels and computed on the concentration of fine particulate matter (PM2.5), the dominant pollutant during haze episodes, along with other pollutants.

24 - Hour PSI

To assess the situation and plan ahead, use the air quality indicators that are based on an average of a 24-hour period and are related to scientific studies on the effects of particulate matter, duration of exposure and health.

PSI Value
Air Quality
0 - 50
51 - 100
101 - 200
200 - 300
Very Unhealthy
Above 300

1 - Hour PM2.5

During the haze season, the main air pollutant is PM2.5. Hence, the 1-hour PM2.5 concentration readings are a good indicator of the current air quality.

NEA has introduced new bands and descriptors for the 1-hour concentration readings for PM2.5. Use the 1-hour PM2.5 figures to plan for immediate activities, like going for a jog.

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Haze & Health

The health impact of haze is dependent on each person’s quality of health, the PSI level, and the length as well as intensity of outdoor activity. Reducing outdoor activities and physical exertion can help limit the ill effects from haze exposure.

When the air quality forecast is in the range of unhealthy and upwards, healthy persons should reduce or avoid prolonged and strenuous outdoor physical exertion. The elderly, pregnant women and children should minimise outdoor activity, while those with chronic lung or heart disease should avoid outdoor activity. Persons who are not feeling well, especially the elderly and children, and those with chronic heart or lung conditions, should seek medical attention.

PSI readings

The PSI readings reflect a total of six pollutants - sulphur dioxide (SO2), particulate matter (PM10), fine particulate matter (PM2.5), nitrogen dioxide (NO2), carbon monoxide (CO) and ozone (O3).

The air quality in Singapore is monitored through a network of air monitoring stations located in different parts of the island and is based on air quality reporting systems used by various countries that incorporate in their index, PM2.5 concentrations, which is considered an important component of air quality that impacts health.