# Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008 on ambient air quality and cleaner air for Europe, Division 2: Criteria

Extent: E+W+S+N.I.

The following criteria shall be used for checking validity when aggregating data and calculating statistical parameters:
In cases where all possible measured data are not available, the following factor shall be used to calculate AOT40 values:
AOT40estimate = AOT40measured ×
total possible number of hours (*)
number of measured hourly 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 value
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)

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Source: https://www.legislation.gov.uk/eudr/2008/50/annex/VII/division/A/division/2 (the official version)
Page: https://openlegislation.uk/eu-directive-2008-50/annex-VII/division-A/division-2
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.