Overview
ISO 21258:2010 specifies a reference method for determining the mass concentration of dinitrogen monoxide (N2O, nitrous oxide) in flue gas from ducts and stacks using the non-dispersive infrared (NDIR) technique. The standard covers sampling, sample conditioning, analyser requirements and performance evaluation. It is intended for periodic monitoring and for the calibration, adjustment or control of automatic monitoring systems permanently installed on stacks. The method has been validated in practice (e.g., a sewage sludge incinerator with N2O up to about 200 mg/m3).
Keywords: ISO 21258:2010, N2O, nitrous oxide, NDIR, stationary source emissions, flue gas monitoring, reference method.
Key topics and technical requirements
- Principle and analytical technique
- Use of NDIR analysers for selective detection of N2O in stack gases.
- Sampling and sample conditioning
- Requirements for probe, sampling line and conditioning system to deliver representative, interference-free gas to the analyser.
- Automated measuring equipment
- Description of analyser components, sampling line components and responsibilities for operation and maintenance.
- Performance criteria and uncertainty
- Procedures for determining performance characteristics (repeatability, reproducibility, response time) and establishing an uncertainty budget in line with ISO measurement guides.
- Measurement procedure
- Guidance on sampling location, sampling points, on-site analyser setup and residence/response time considerations.
- Quality control and field evaluation
- Ongoing QC checks, frequency of checks, field evaluation, expression of results and reporting requirements.
- Supporting normative and informative annexes
- Schematics (Annex A), test procedures for performance characteristics (Annex B), compliance examples, comparison test results and leak test procedures.
Keywords: sampling conditioning, performance criteria, measurement uncertainty, QC, response time.
Practical applications and users
- Who uses ISO 21258:2010
- Environmental laboratories performing stack emission testing.
- Plant operators and engineering teams responsible for continuous emissions monitoring systems (CEMS).
- Regulatory bodies and auditors verifying compliance with emission inventories or trading schemes.
- Equipment manufacturers and integrators designing NDIR-based N2O analysers and sampling systems.
- Where it’s applied
- Periodic emission monitoring, CEMS calibration and performance verification at incinerators, power plants, industrial boilers and processes where nitrogenous fuels or SNCR denitrification are used.
- Why it matters
- N2O is a potent greenhouse gas (≈310× global warming potential of CO2); accurate measurement reduces uncertainty in emission inventories and supports regulatory programs.
Keywords: stack monitoring, CEMS calibration, industrial emissions, greenhouse gas monitoring.
Related standards
- ISO 9169:2006 - performance characteristics of automatic measuring systems
- ISO 14956 - evaluation of measurement procedures vs required uncertainty
- ISO/IEC Guide 98-3:2008 (GUM) - expression of measurement uncertainty
Using ISO 21258:2010 helps ensure standardized, traceable N2O measurements for regulatory compliance, instrument calibration and robust emission inventories.