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Key Takeaways

Some key takeaways of the new OTM-50 method:

• provides a consistent method to measure PFAS in air emissions
• collects gas samples to measure for VFCs in 6-liter passivated silicon ceramic-lined stainless-steel canisters
• samples industrial source ducts, vents, stacks, etc.
• can be used by chemical manufacturers, industrial users of PFAS, and destruction technologies

Additionally, although not officially adopted by the U.S. EPA, the Agency encourages the use of the new OTM-50 method for development of data, which could lead to development of emissions standards, including for PFAS.

Introduction

In mid-January 2024, the United States Environmental Protection Agency (U.S. EPA or Agency) published a new method to assist in measuring substances such as per- and polyfluoroalkyl substances (PFAS) in air emissions. The new method is known as “Other Test Method 50” or “OTM-50.” While the Agency did not officially publish the draft method, it released the method to promote consistency in sampling of PFAS.

Background on U.S. EPA’s Other Test Methods

When a test method is posted on the Other Test Method (OTM) portion of the Air Emission Measurement Center (EMC) website, the U.S. EPA does not endorse the validity of the test, and it is not a regulatory approval of the test method.[1] The purpose of the OTM portion of the EMC website is to promote discussion of developing emission measurement methodologies and to provide regulatory agencies, the regulatory community, and the public at large with potentially helpful tools. OTMs are test methods that have not yet been subject to the Federal rulemaking process.

OTMs and the technical documentation supporting them have been reviewed by EMC staff and have been found to be potentially useful to the emission measurement community. Along with these OTMs, the U.S. EPA strongly encourages the submission of additional supporting field and laboratory data as well as comments regarding these methods. These methods may be considered for use in federally enforceable state and local programs provided they are subject to a U.S. EPA Regional SIP approval process or permit veto opportunity and public notice with the opportunity for comment.

Reasons for Development of OTM

Development of methods to measure PFAS is an ongoing process for the U.S. EPA. Measurements methods that have been evaluated for identifying and quantifying PFAS or volatile fluorinated compounds (VFCs) releases from stational air emissions sources are limited and under development. There is a lack of standardized source measurement of PFAS and VFC emissions, which leads to uncertainty in understanding these emission releases and further leads to inconsistent findings, incomparable measurements, and a lack of coordination between policy makers, facilities, and control technology development. OTM-50 helps provide a consistent method for use by the facilities, stationary source test teams, research laboratories, and other stakeholders to measure a common list of VFCs emitted from vents and stacks.

The OTM-50 testing methods could also provide a foundation for U.S. EPA to begin to shape air emissions standards for PFAS under the Clean Air Act or other regulations. The U.S. EPA is currently in a data collection phase for determining how to approach the question of drafting air emissions standards for PFAS. OTM-50 will assist the Agency in gathering further data and ensuring that any future air emissions levels are able to be tested by industries.

The OTM-50 Methodology

The OTM-50 is a performance-based method applicable to the collection and quantitative analysis of specific VFCs. OTM-50 incorporates other methods by reference. For example, source sampling teams should be trained and have experience with U.S. EPA Method 1, Method 2, Method 3, and Method 4. Laboratory analysis teams should be trained and experienced in the use of gas chromatography coupled with mass spectrometry as described in U.S. EPA compendium Method TO-15A and ASTM D5466-21, Standard Test Method D5466-21. Further, field sampling and recovery staff must be trained in the best practices for extracting representative gas samples from an emission vent or stack, conditioning the gas if necessary to manage moisture and acid gases, and collecting the gas sample in passivated stainless-steel canisters.

The OTM-50 method is used to collect and analyze gas samples into 6-liter passivated silicon ceramic-lined stainless-steel canisters, or equivalent, from stationary sources for the purpose of determining the concentration of target VFCs. The gaseous emissions samples collected by the method are intended to be sampled from industrial source ducts, vents, stacks, etc. Further, the test method is applicable to VFC concentrations in undiluted samples ranging from the detection limit to approximately 100 µg/m³, 300 parts-per-billion by volume (ppbv).

The OTM-50 method provides that gas samples are collected from a sampling manifold using evacuated canisters equipped with a critical orifice for sample flow control. Samples are collected directly from the manifold with or without a water and acid gas management system. Measurements of stack carbon dioxide (CO₂) are also required. The volumetric concentration of CO₂ is important information for the proper preparation of calibration standards and analytical laboratory method optimization.

The source moisture concentration is necessary to determine what sampling train configuration is appropriate. The volumetric moisture concentration is also needed to calculate results on both a wet and dry basis. Water and CO₂ measurements in conjunction with stack or duct volumetric flows are required as part of this method. VFCs are identified and quantified in gas samples from canisters by gas chromatography coupled with mass spectrometry. Additional volatile compounds present in canister samples that are not on the target list are reported with their best-available matches to mass spectral reference libraries.

The OTM-50 can be used by chemical manufacturers, industrial users of PFAS and destruction technologies, and could certainly be expanded for use by other industry types in the future as the U.S. EPA’s understanding of air emissions issues and reliable testing methods evolves.

[1] https://www.epa.gov/system/files/documents/2024-01/otm-50-release-1_0.pdf; see also https://www.epa.gov/emc/emc-other-test-methods.