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Looking at trends over the past 3 days and comparing it to the popular AQI figure derived from 1 hour PM2.5.
- NEA official calculation of PSI does NOT include 1 hour PM2.5. It uses 24 hour PM2.5.
- The different inputs and the smoothing calculations underlying PSI are why AQI and PSI are out of sync.
- The conversion of 1hr PM2.5 used here and elsewhare on the web is based on the EPA AQI Calculator which is intended for an input of 24 hour PM2.5. There is no official conversation of 1hr PM2.5 to AQI so this is a proxy.
- Health warnings based on AQI PM2.5 are not strictly reliable: health warnings have been established for 24hour PM2.5, not 1hr PM2.5. Saying that, health warnings are not an exact science either way.
- The risk advisories based on AQI are a satisfactory benchmark for personal decisions but given the volatility of 1hr numbers and lack of research on the health risks of very short term exposure, the AQI is presently an inappropriate metric for policy decisions.
TLDR: AQI is suitable for personal decision making only. It is not intended as a substitute for PSI.