Work out air quality index instantly with clear inputs, formula shown and shareable results.
The US EPA AQI maps PM2.5 concentration onto a 0-500 scale through piecewise linear breakpoints, so 35 ug/m3 gives an AQI of 99 - the top of the moderate band. That is more than twice the WHO 24-hour guideline of 15 ug/m3, which is stricter than the EPA breakpoints and is why national indices and WHO advice often disagree.
EPA AQI interpolation
AQI = (Ihigh - Ilow) / (Chigh - Clow) x (C - Clow) + Ilow
PM2.5 breakpoints
0-12 good, 12.1-35.4 moderate, 35.5-55.4 unhealthy for sensitive groups
Because each sets its own breakpoints and averaging periods. India, China, the EU and the US all use different scales.
No - ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide and PM10 are each converted and the highest sub-index becomes the reported AQI.