preamble_98

Sampling must be continuous although breaks of a few minutes each day or week are permissible to enable filters to be changed. An annual mean value will not be considered valid unless sampling has occurred on a minimum of 10 working days per month, during the first five years after the notification of the Directive and on a minimum of 15 working days per month thereafter, as far as possible, evenly spread over the period under consideration. The mean annual value is calculated by dividing the sum of the valid daily values by the number of days on which valid values have been obtained.

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Source: EUR-Lex (Cellar) · retrieved 2026-11-07 · Text as adopted (Official Journal); later amendments are not incorporated in this text.