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 1-hour PM2.5 reading, on the other hand, is the hourly average of the PM2.5 pollutant levels. PM2.5 is fine particulate matter with a diameter of 2.5 micrometres or shorter, and is the dominant pollutant during haze that causes harm to health.
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