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EPA Traceability Protocol for Assay and Certification of Gaseous Calibration Standards

What is the EPA Traceability Protocol for Assay and Certification of Gaseous Calibration Standards?

The Traceability Protocol for Assay and Certification of Gaseous Calibration Standards is used to certify calibration gases for ambient and continuous emission monitors. It specifies methods for assaying gases and establishing traceability to National Institute of Standards and Technology (NIST) reference standards. Traceability is required under EPA ambient and continuous emission monitoring regulations.

The protocol was developed jointly by EPA, NIST, the auto industry, and specialty gas producers to address concerns about commercial calibration gas accuracy and stability. Gases produced in line with this protocol are referred to as “EPA Protocol Gases.” Specialty gas producers are required to participate in EPA protocol gas verification programs (PGVP) to refer to these gases in this manner. 

Who should use the protocol?

Specialty gas producers use the protocol to analyze and certify gases sold to electrical utilities, state air pollution control agencies, and other end users. Similarly, end users and PGVP laboratories use the EPA protocol to verify the certified concentrations of EPA Protocol Gases. 

How does the protocol work?

The protocol is designed to minimize systematic and random errors in the assay and certification process. Specialty gas producers follow the protocol when preparing and certifying EPA Protocol Gases. EPA PCVPs verify the quality of these gases by conducting blind tests of samples purchased from the producers' routine production. The results are made publicly available. This approach balances the government’s need for accuracy with the producers’ need for flexibility, low cost, and minimum external oversight. 

What are the benefits of the protocol?

  • Used to meet regulatory requirements
  • Enhances good decision-making / reporting
  • Supports private sector production
  • Ensures compressed gases used to calibrate air pollution monitors are consistent for reliable monitoring
  • Ensures that regulatory decisions about attainment of air pollution standards are correct
  • Ensures emissions trading programs are priced fairly 
  • Ensures the quality of the measurements used with these gases is accurate


US EPA (2012) “Traceability Protocol for Assay and Certification of Gaseous Calibration Standards” (PDF) (174 pp, 1.7 M, About PDF) Publication No. EPA/600/R-12/53.

Other Resources

A Broad Overview of EPA Protocol Gases (Presentation)

Technical Aspects of EPA Protocol Gas Production (Presentation)

Compilation of Various Questions and Answers about EPA Traceability Protocol for Gaseous Calibration Standards

NO2 Cylinder Guidance for State-Local Agencies and Gas Producers

Protocol Gas Verification Programs

Technical Contact

Robert S. Wright (
Phone: 919-541-4502