The Air Quality Standards Regulations 2007

PART 2 Criteria for aggregating data and calculating statistical parameters

4.  In this Part, percentiles are to be calculated using the method specified in Council Decision 97/101/EC(1) establishing a reciprocal exchange of information and data from networks and individual stations measuring ambient air pollution within member States.

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 2(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, 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 (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 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)

(1)

OJ L 35, 05.02.97, p.14.