# The Air Quality (Ozone) (Wales) Regulations 2003, Part II: Criteria for aggregating data and calculating statistical parameters


In this Part, percentiles are to be calculated using the method specified in Council Directive 97/101/EC.
The following criteria are to be used for checking validity when aggregating data and calculating statistical parameters:
Parameter
Required proportion of valid data
(a)in cases where all possible measured data are not available, the following factor must be used to calculate AOT40 values:
AOT40(estimate)=AOT40(measured)×totalpossiblenumberofhours*number of measured hourly values *being the number of hours within the time period of AOT40 definition (that is, 8:00 to 20:00 Central European Time from 1 May to 31 July each year, for vegetation protection and from 1 April to 30 September each year for forest protection).
1 hour values
75% (45 minutes)
8 hour values
75% of values (6 hours)
Maximum daily 8 hours mean from hourly running 8 hours averages
75% of the hourly running 8 hour averages (8 hours per day)
AOT40
90% of the 1 hour values over the time period defined for calculating the AOT40
Annual mean
75% of the 1 hour values over summer (April to September) and winter (January to March, October to December) seasons separately
Number of exceedances and maximum values per month
90% of the daily maximum 8 hours mean value (27 available daily values per month) 90% of the 1 hour values between 8:00 and 20:00 Central European Time
Number of exceedances and maximum values per year
Five out of six summer months over the summer season (April to September)

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Source: https://www.legislation.gov.uk/wsi/2003/1848/schedule/8/part/II (the official version)
Page: https://openlegislation.uk/air-quality-ozone-wales-regulations-2003/schedule-8/part-II
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.