Overview
ISO 11222:2002 - Air quality: Determination of the uncertainty of the time average of air quality measurements specifies a method to quantify the uncertainty of a time average computed from air quality data collected at a single location over a defined averaging period. The method applies to continuous or intermittent monitoring and follows the recommendations of the Guide to the Expression of Uncertainty in Measurement (GUM). It separates uncertainty contributions from the measuring system and from incomplete time coverage of the data set, and guides calculation of combined and expanded uncertainty for reporting.
Key topics and requirements
- Scope and applicability
- Applies when the data set is representative of the temporal structure of the measurand, measurement-uncertainty information is available, and all results come from the same location.
- Covers time averages of scalar measurement results (e.g., hourly, daily, monthly means).
- Main uncertainty contributions
- Measuring-system-induced uncertainty (instrument bias, calibration, procedural factors).
- Uncertainty due to incomplete time coverage (gaps or intermittent sampling that do not fully capture temporal variability).
- Methodology
- Implements GUM principles: estimate standard uncertainties, combine them (combined standard uncertainty), apply a coverage factor to obtain expanded uncertainty at a stated confidence level.
- Addresses degrees of freedom and how they affect the coverage factor for expanded uncertainty.
- Data and reporting requirements
- Requirements on input data (representativeness, number and timing of measurements).
- Reporting guidance for the time average and its uncertainty so results are reproducible and comparable.
- Support material
- Informative Annex A provides an example application (monthly average of nitrogen dioxide).
Applications and users
ISO 11222 is practical for organizations that produce, evaluate or use time-averaged air quality data:
- Environmental monitoring agencies and regulatory bodies assessing compliance with air-quality standards.
- Laboratory and field measurement teams designing monitoring campaigns (continuous or intermittent).
- Air quality modelers and data analysts who require quantified uncertainty on time-averaged inputs or validation data.
- Quality assurance / quality control (QA/QC) specialists setting data-quality objectives and performance criteria.
Benefits include more transparent compliance decisions, defensible reporting of averages (hourly, daily, monthly), and consistent handling of gaps and instrument-related uncertainty.
Related standards
- GUM:1995 - Guide to the expression of uncertainty in measurement (normative reference used by ISO 11222).
- References in ISO 11222 also include statistical and metrology documents (e.g., VIM, ISO 3534-1) used for definitions and terms.
Keywords: ISO 11222:2002, air quality, uncertainty of time average, measurement uncertainty, GUM, continuous monitoring, intermittent monitoring, incomplete time coverage.
