This paper assesses the problem of the calculation of an averaging uncertainty for measurements in the framework of
the European Air Quality Directives. Current environmental legislation establishes maximum uncertainties associated
with a defined period of measurements. The difficulties of an ‘a priori’ determination of uncertainty contributions
associated with both the averaging of measurements and an incomplete time series are discussed. The definition of an
overall uncertainty, which includes budget contributions from the afore-mentioned factors, is not helpful as a
regulatory parameter for quality. Alternatively, it should be used as additional information to associate with the
average measurement value. This should be taken into consideration in future revisions of the European ambient air
quality legislation.JRC.H.4-Transport and air qualit