API or AQI? Why other apps show a different number
Updated 2 min read
You open two apps in the same hour and get two numbers. One says 93, the other says 124. Neither is wrong. They are reading off different tables.
One concentration, two tables
Malaysia's API and the American AQI start from the same thing: a 24-hour average concentration of a pollutant. What differs is the table that turns that concentration into an index number, and Malaysia's is more forgiving through the middle.
| PM2.5 (µg/m³) | Malaysian API | US AQI |
|---|---|---|
| 25 | 68 — Moderate | 78 — Moderate |
| 35 | 80 — Moderate | 99 — Moderate |
| 45 | 93 — Moderate | 124 — Unhealthy for Sensitive Groups |
| 55 | 146 — Unhealthy | 149 — Unhealthy for Sensitive Groups |
| 75 | 161 — Unhealthy | 161 — Unhealthy |
Notice where the gap sits. On genuinely bad air the two nearly agree. The gap is widest on a middling day, between 12 and 50 µg/m³, because Malaysia's 51–100 band stretches to 50.4 µg/m³ where the American one ends at 35.4.
Second reason: some apps do not wait 24 hours
The official API is computed from a 24-hour average. Some apps display an hourly value instead, so the figure moves faster. An hourly value spikes higher in the evening and falls away sooner overnight, which makes it look more alarming without making it more accurate.
Third reason: where the data comes from
Several international apps do not read the Department of Environment's stations at all. They use a model, satellite data or consumer sensors, then publish the result as a city value. Models can be well off when smoke is moving quickly.
SemakAPI publishes the Department of Environment's official API value as issued, with no recalculation. If the number here differs from another app, that app is most likely showing the US AQI or a modelled value.
Which one to follow
In Malaysia, follow the API. It is the figure official instructions are written against: school closures, open burning bans and health warnings all reference the API, not the AQI.