The Air Quality Standards (Scotland) Regulations 2007

5.  The following criteria are to be used for checking validity when aggregating data and calculating statistical parameters–

Parameter	Required proportion of valid data
(1) In this table “AOT40” has the same meaning as in paragraph 3(d) of Part 4 of Schedule 1.
(2) In cases where all possible measured data are not available, the following factor shall be used to calculate AOT40 values: AOT40 (estimate) = AOT40 measured x (total possible number of hours ÷ number of measured hourly values). The reference in this formula to the total possible number of hours is to the hours within the time period of AOT40 definition (that is, 08:00 to 20:00 Central European Time from 1st May to 31st July each year, for vegetation protection and from 1st April to 30th 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 (18 8 hours averages per day)
AOT40(1)	90% of the 1 hour values over the time period defined for calculating the AOT40 value(2)
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 08:00 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)