AOT40 (expressed in (μg/m3) · hours) means the sum of the difference between hourly concentrations greater than 80 μg/m3 (= 40 parts per billion) and 80 μg/m3 over a given period using only the one-hour values measured between 8.00 and 20.00 Central European Time (CET) each day.
The following criteria shall be used for checking validity when aggregating data and calculating statistical parameters:
| a In cases where all possible measured data are not available, the following factor shall be used to calculate AOT40 values:
(*)being the number of hours within the time period of AOT40 definition, (i.e. 08:00 to 20:00 CET from 1 May to 31 July each year, for vegetation protection and from 1 April to 30 September each year for forest protection). | ||||
| Parameter | Required proportion of valid data | |||
|---|---|---|---|---|
| One hour values | 75 % (i.e. 45 minutes) | |||
| Eight hours values | 75 % of values (i.e. six hours) | |||
| Maximum daily 8 hours mean from hourly running 8 hours | 75 % of the hourly running eight hours averages (i.e. 18 eight-hourly averages per day) | |||
| AOT40 | 90 % of the one hour values over the time period defined for calculating the AOT40 valuea | |||
| Annual mean | 75 % of the one hour values over summer (April to September) and 75 % over winter (January to March, October to December) seasons separately | |||
| Number of exceedances and maximum values per month | 90 % of the daily maximum eight hours mean values (27 available daily values per month) 90 % of the one hour values between 8.00 and 20.00 CET | |||
| Number of exceedances and maximum values per year | five out of six months over the summer season (April to September) | |||