ISO 14956:2002

Overview

ISO 14956:2002 - "Air quality - Evaluation of the suitability of a measurement procedure by comparison with a required measurement uncertainty" - provides a standardized procedure to judge whether an air quality measurement method meets a specified required measurement uncertainty. It is intended for measurement procedures whose output is a defined time average and complements existing guidance (for example ISO 6879 and the GUM on uncertainty propagation).

The standard defines how to estimate uncertainty from a method’s performance characteristics (laboratory claims or actual data), how to assess dynamic behaviour, and how to verify suitability by field testing.

Key Topics and Requirements

• Estimation of measurement uncertainty: Use reported or experimentally determined performance characteristics and the GUM propagation approach to calculate combined and expanded uncertainties for the measurand.
• Performance characteristics: Convert repeatability, reproducibility, bias, drift, interferent sensitivity and other characteristics into partial standard uncertainties, assign them to input quantities, then propagate to the measured value.
• Dynamic behaviour: Define and demonstrate instrument response time and dynamic conditions; show the dynamic contribution to uncertainty is negligible or otherwise accounted for.
• Stationary conditions: Define analytical/model and variance functions, identify influence quantities, and quantify operating conditions and uncertainty contributions under steady-state operation.
• Field verification: Confirm laboratory performance in real-world conditions and document results.
• Reporting: Require clear definition of the measurand, steps included (sampling, calibration, postprocessing), and presentation of uncertainty estimates and compliance judgements.

The standard includes informative and normative annexes (default interferent ranges, coverage factors, worked examples such as UV fluorescence SO2 assessment, and sample field verification programmes).

Applications and Who Uses ISO 14956

ISO 14956 is practical for:

• Environmental laboratories validating air quality measurement methods
• Instrument manufacturers specifying performance and dynamic response
• Regulatory bodies and compliance auditors assessing methods against legal measurement quality requirements
• Consultants and researchers designing monitoring networks and specifying time-averaged measurement outputs
• QA/QC teams performing field verification and method acceptance

Typical uses: method selection, uncertainty budgeting, compliance demonstration, instrument procurement specifications, and preparing method validation reports.

Related Standards

• ISO 6879:1995 - performance characteristics and related concepts for air quality measuring methods (normative reference)
• The GUM (Guide to the Expression of Uncertainty in Measurement) - underlying propagation methodology

Keywords: ISO 14956, air quality measurement, measurement uncertainty, performance characteristics, dynamic behaviour, time average, field verification, calibration.