Pollutant Standards Index

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The Pollutant Standards Index (PSI) is a type of air quality index used in Singapore, which is a number used to indicate the level of pollutants in air. Initially PSI was based on five air pollutants, but since 1 April 2014 it has also included fine particulate matter (PM2.5). In addition to the PSI derived by averaging data collected for the past 24 hours, Singapore also publishes 1-hr PM2.5 concentrations every hour. Besides Singapore, some other countries also use air quality indices. However, the calculations used to derive their air quality indices may differ. Different countries also use different names for their indices such as Air Quality Health Index, Air Pollution Index and Pollutant Standards Index.

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