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) | |||
| a Compliance with target values will be assessed as of this date. That is, 2010 will be the first year the data for which is used in calculating compliance over the following three or five years, as appropriate. | |||
| b The maximum daily eight-hour mean concentration shall be selected by examining eight-hour running averages, calculated from hourly data and updated each hour. Each eight -hour average so calculated shall be assigned to the day on which it ends. i.e. the first calculation period for any one day will be the period from 17:00 on the previous day to 01:00 on that day; the last calculation period for any one day will be the period from 16:00 to 24:00 on the day. | |||
| c If the three or five year averages cannot be determined on the basis of a full and consecutive set of annual data, the minimum annual data required for checking compliance with the target values will be as follows:
| |||
| Objective | Averaging period | Target value | Date by which target value should be meta |
|---|---|---|---|
| Protection of human health | Maximum daily eight-hour meanb | 120 μg/m3 not to be exceeded on more than 25 days per calendar year averaged over three yearsc | 1.1.2010 |
| Protection of vegetation | May to July | AOT40 (calculated from 1 h values) 18 000 μg/m3 · h averaged over five yearsc | 1.1.2010 |
| Objective | Averaging period | Longterm objective | Date by which the longterm objective should be met |
|---|---|---|---|
| Protection of human health | Maximum daily eight-hour mean within a calendar year | 120 μg/m3 | not defined |
| Protection of vegetation | May to July | AOT40 (calculated from 1 h values) 6 000 μg/m3 · h | not defined |