My question is specifically about the UK and their COMEAP Air Quality Index (AQI) scale, but it probably applies more widely - though the answers may be different.
AQI values for the UK are a 24 hour measurement, and for any moment in time we can quote a rolling 24 hour number for the AQI.
But when the AQI is either forecast for future days, or recorded for past days what is the value that is quoted?
The highest rolling 24 hour AQI value of the day?
The mean of the rolling AQI values for the day?
The AQI for the 24 hours of that day - i.e. the value at 23:59?
The AQI at midday?
Or...?