This International Standard specifies, for the field of air quality procedures, the: - estimatation of measurement uncertainty from actual or claimed values of all important performance characteristics of a method under stationary conditions; - assessment of whether or not specified values for these performance characteristics comply with the required quality of a measured value at a stated measure and value; - evaluation of the applicability of the measurement method based on laboratory performance and confirmatory field test; - establishment of requirements on dynamic behaviour of instruments. This International Standard is applicable to measurement procedures whose output is a defined time average.