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Clean Air Markets

Protocol Gas Verification Program (PGVP)


On and after May 27, 2011, the owner or operator of a unit subject to Part 75 emissions monitoring that uses EPA Protocol gases must procure the gases from a production site that is listed as a PGVP participant on the date that it procures the gases, or from a merchant who sells unaltered EPA Protocol gases produced by an EPA Protocol gases production site that is listed as a PGVP participant on the date that the merchant procured the gases.  See 40 CFR 75.21(g)(6) and (7). These gases and the associated quality assurance/quality control (QA/QC) checks help ensure the quality of the emission data that EPA uses to assess achievement of emission reductions required under the Clean Air Act.

The PGVP has four main objectives: (1) to ensure that EPA Protocol gases meet the accuracy requirements of 40 CFR Part 75; (2) to assist calibration gas consumers in their purchasing decisions; (3) to provide an incentive for gas vendors that perform well in the audits to continue to use good practices; and (4) to encourage gas vendors that perform poorly in the audits to make improvements.

2019 Participants and Vendor IDs

The list of current participants in EPA's Protocol Gas Verification Program (PGVP) for stationary source monitoring is updated: (1) at the beginning of each calendar year; (2) when an EPA Protocol gas production site joins the program; (3) when the information for a listed production site changes; or (4) when a production site is removed from the list. The vendor IDs are production site-specific and are the same ones that are used in the PGVP for ambient air monitoring, which is run by EPA's Office of Air Quality Planning and Standards.

PGVP Participants:


The following reporting instructions apply only to EPA Protocol gas production sites and specialty gas companies that wish to participate in the Protocol Gas Verification Program (PGVP) for stationary source monitoring. Organizations interested in participating in the PGVP for ambient air monitoring, which is run by EPA's Office of Air Quality Planning and Standards (OAQPS) in Research Triangle Park, North Carolina, should go to the National Performance Evaluation Program – Ambient Air Protocol Gas Verification Program Web page.

An EPA Protocol gas production site that chooses to join the PGVP initially, or to continue its participation in the PGVP from year-to-year, must notify EPA via email. Notification of intent to initially participate may be sent at any time. Notification to continue participating in the next calendar year must be sent by December 31st of the current year. Send all notifications to the following address: Each notification must include the following information (a PGVP Participation Request Form is also available):

  • The name and address of the production site;
  • The name, email address, and telephone number of a contact person for the production site;
  • The name of the specialty gas company that owns or operates the production site; and
  • The name, email address, and telephone number of a contact person for that specialty gas company.

A production site's participation commences immediately upon notification to EPA and extends through the end of the calendar year for which notification is provided. EPA will issue a vendor ID to each participating production site.

Reporting Instructions

The PGVP reporting instructions are incorporated into the ECMPS reporting instructions.

Audit Results

2013 Results at a Glance

Category Amount
Number of Samples 240
Number of Failures 5
Passing Percent 98%
Number of Production Sites 20
Number of Production Sites that Failed 4
Percent of Production Sites that Failed 20%
Number of Participating Vendors 11
Number of Vendors that Failed 4
Percent of Vendors that Failed 36%
Number of Protocol Gas Audit Failures
   CO2   NO   SO2 
High   1  
Mid   1  
Low   1 2

Download the 2010 and 2013 Full Audit Reports
Download 2013 Summary Results Table.xlsx(1 pg, 13 K)

The U.S. Environmental Protection Agency (EPA) conducts blind audits of EPA protocol calibration gas cylinder mixtures produced by specialty gas manufacturers.

The objective is to determine the concentration of the analytes in cylinder mixtures and to compare the quantified values with those stated in the certificates of the supplying producer. The quality of these calibration mixtures is critical for the accurate determination and reporting of regulated gaseous emissions.

In the Environmental Protection Agency Blind Audit 2013, the National Institute of Standards and Technology (NIST) analyzed 240 calibration gases between 2013 and 2015. The mixtures were tri-blends of Carbon Dioxide (CO2; range: 5% mol/mol – 20% mol/mol); Nitric Oxide (NO; range: 25 µmol/mol – 1000 µmol/mol (ppm) and Total Oxides of Nitrogen, NOX, within 1% relative of NO) and Sulfur Dioxide (SO2; range : 50 µmol/mol – 1000 µmol/mol (ppm)).

The 2013 audit of EPA Protocol gases found a 2.1% failure rate over all components analyzed, with 15% of the production sites failing at least one gaseous component. The Report of Analysis was compiled by NIST and released on April 21, 2015.

A similar, but unrelated audit was conducted in 2008 for the EPA Office of Inspector General and an EPA blind audit was conducted in 2010. The full 2010 and 2013 audit reports are available at Protocol Gas Verification Program Audit Reports.

Chart showing the results of the 2013 Protocol Gas Audit

General Testing Procedures

Without informing the production site that a blind sample of their cylinders was being audited, three cylinders per production site were purchased by a company that normally purchases these types of cylinders. The cylinders in the sample were analyzed by the National Institute of Standards and Technology (NIST). Within each parameter (NO, SO2, CO2), all low concentrations were essentially identical, all mid concentrations were essentially identical, and all high concentrations were essentially identical.

The above audit results are for the cylinder original concentration for each component and do not include any re-analyses that may have been performed by a production site. The rationale for including summary results for only original tag values is that gas cylinder purchasers will receive cylinders with tag values based on original analysis, not re-analysis, so it is important for a gas production site to produce an accurately labeled cylinder the first time. Please see the full audit report for more complete information and for any re-analyses and corrective actions performed by a production site.

A gaseous component is said to fail when the absolute value of the difference between the audit and vendor concentration values is greater than 2.20%. The 2.20% value is determined by using the "paired t test" at 95% confidence, with an uncertainty of plus or minus 2.0% (fixed by Part 75, Appendix A, section 5.1.4(b)) for the gas vendor and an expanded uncertainty (coverage factor k=2) of plus or minus 1.0% (maximum acceptable) for the audit. If on future audits, e.g., for very low concentration gases, the plus or minus 1.0% audit expanded uncertainty value changes, the 2.20% value may change. If the absolute value of the difference between the audit value and the vendor value is 2.20% or less, then (because of the uncertainties in the total measurement system) statistically there is no difference between the two values. Thus, a difference of 2.10% would be interpreted as being equal to one of, for example, 0.40%.

Nothing can be said regarding the performance of any EPA Protocol gas production site not included in the audit. Any accuracy assessment is an instantaneous snapshot of the process being measured. These results should not be regarded as a final statement on the accuracy of EPA Protocol gases. They can be used as a general indicator of the current status of the accuracy of EPA Protocol gases as a whole. However, individual results should not be taken as definitive indicators of the analytical capabilities of individual producers. EPA presents this information without assigning a rating to the gas vendors, and specifically does not endorse any particular vendor.

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