Update on Protocol Gas Certification for use in Source Measurements

On March 11, 2024, the U.S. Environmental Protection Agency (U.S. EPA) issued a memorandum addressing “Accepted Use of Protocol Gases that are Recognized for Regulatory Use.” The memo was authored by staff members from both the Office of Air Quality Planning and Standards and the Center for Environmental Measurement and Modeling and was addressed to Regional Directors in the Offices of Air and Radiation and Enforcement and Compliance Assurance.

“Protocol Gases” are specialty gas mixtures used for calibration of air measurement systems. U.S. EPA developed a series of specifications for gases to be used in calibration or other quality activities associated with emissions and ambient gas measurements.

Bottom Line: For source applications and monitoring, mixtures of sulfur dioxide in air and nitrogen dioxide in nitrogen can be used as Protocol Gases. In short, for these applications, there are no issues with using these gases, and they can be acquired and used as they have historically been acquired and used.

Longer Version: In February 2022, U.S. EPA released a memo noting that gases prepared with sulfur dioxide in air, or nitrogen dioxide in nitrogen did not have enough long-term stability for use demonstrating compliance with the National Ambient Air Quality Standards (NAAQS) under 40 CFR Parts 50 and 58. According to that memo, these gases could not be certified as “protocol gases.” As a result, specialty gas providers were not documenting these gases as meeting the appropriate specifications and end users were in a bit of a quandary. The requirements to perform testing or to monitor emissions had not changed. Yet, the calibration gases that had been used were unavailable; or more correctly, the vendors could not certify the gases as meeting U.S. EPA’s specifications.

Unfortunately for everyone involved, the language of the 2022 memorandum did not discern between ambient measurements and source measurements. While there is truly a technical issue with gases prepared at levels appropriate for ambient measurements, there is no stability issue for gases prepared at levels appropriate for source emissions. The new memorandum (March 2024) clarifies that the “protocol gases” can be prepared and used for source measurement and monitoring under 40 CFR Parts 59, 60, 61, 63, and 65.

An Eye to the Future: The March 2024 memo goes on to recognize that the Protocol Gas Program needs to be updated. U.S. EPA intends to take the necessary time to review and update regulations, and to provide appropriate clarity and transparency to the guidance documents. They have set up a Protocol Gas mailbox (protocol-gas-program@epa.gov) to respond to any questions or comments while they work through the updates.

ALL4 will continue to monitor this situation and provide updates as appropriate. If you have any questions or concerns on this topic, please feel free to reach out at:

Gene Youngerman: eyoungerman@all4inc.com, 512.649.2571.