New Testing and Measurement Techniques for Detecting Airborne PFAS

By Ryan Moffet, PhD

We published an overview of Per- and Polyfluoroalkyl Substances (PFAS) testing techniques in March 2022, and while there were several testing methods for detecting PFAS in soil and water at that time, similarly standardized and reliable methods for detecting and monitoring PFAS were just being introduced. The U.S. Environmental Protection Agency’s (EPA) Other Test Method (OTM) 45 was published in January 2021 for the collection and quantification of specific semi-volatile and non-volatile PFAS chemicals at a specific source (sampling from a stack), but this method’s ability to identify a wide range of volatile fluorinated compounds (VFCs, which are a subset of PFAS) is limited.

Updated U.S. EPA Test Method

EPA’s OTM 50 was released in January 2024 to address some of these shortcomings. While this method is still intended to measure emissions at single point sources, such as stacks or vents, the whole-air cannister sampling approach enables facilities and government regulators to determine concentrations of VFCs in the gas phase that may suffer from artifacts when collected via OTM 45.

Importantly, OTM 50 has many of the same limitations of OTM 45. Neither method is conducive to real-time monitoring or ambient measurements, and quality assurance is equally important when using either method as the potential for cross contamination is high from PFAS in testing equipment, clothing, and the ambient atmosphere.

Ambient Measurements

Compendium Method TO-13A can be adapted to sample ambient PFAS, but as it uses sorbent and filters, these samples must still be sent to a lab for workup and analysis. High-resolution mass spectrometry is now widely commercially available, strengthening the chemical identification capabilities for complex environmental samples, such as those collected using method TO-13A. This type of instrumentation is especially powerful for “non-targeted” screening, where standards for each compound are not required. However, challenges still remain due to limitations in chromatography, ionization methods, and limited mass resolving power. The limitation resulting from mass resolving power can stem from the particular mass analyzer used or the complexity of the sample.

As for real-time measurement methods, we mentioned Chemical Ring Down Spectroscopy (CRDS) as a promising technology for this application in our previous blog, but Chemical Ionization Mass Spectrometry (CIMS) has emerged as a more selective approach. Recent examples from peer-reviewed literature indicate that CIMS can monitor down to the parts per trillion (PPT)-range when measuring PFAS in ambient air. While the health risks of PFAS are greater with accumulated exposure over time, real-time monitoring is important to diagnose operational equipment or practices that result in releases. Currently, all of the standardized measurement methods including OTM 45 and OTM 50 indicate the quantity and type of chemical released from a point source, but do not identify when emissions were released or the trends in PFAS emissions.

PFAS can be pervasive in the indoor, or “built” environment. For this reason, it may be necessary to perform measurements inside residential dwellings or in other indoor settings. Method TO-13A is not applicable to these types of sampling environment because it uses noisy, high-volume pumps. As an alternative, low-volume samplers or even passive samplers can be used to achieve measurement goals. Low-volume samplers use sorbent and filters much like high-volume samplers, but the low detection limits necessary for PFAS analysis will take longer to achieve due to the lower volume of air sampled. Passive sampling has the advantage of using no pumps, but cannot distinguish between the gas and particle phase. Low volume and passive sampling can also be useful in outdoor applications where power and space are limited or even non-existent. CIMS can and has been used in an indoor setting, assuming the sampling location is able to provide the (significant) space and power required by the instrument.

Key Takeaways

As mentioned in our recent blog post PFAS Strategic Roadmap Accomplishments and Future Outlook, administrative changes and appointments to the EPA make it unclear whether PFAS testing and regulation will remain a priority in the immediate future. In spite of this, advancements from the past three years and ongoing efforts by private companies and academic researchers to improve real-time ambient measurements will likely continue to improve our knowledge about PFAS chemicals that are being emitted and their impact on the environment and human health.

About the Author

Dr. Ryan Moffet is an expert in atmospheric measurements and has extensive experience conducting field measurements designed to address atmospheric science questions. Much of Dr. Moffet’s work has focused on determining the chemical and physical properties of individual aerosol particles using advanced instrumental methods. He has been working on projects involving fenceline monitoring of petroleum operations using open-path measurements, and applying low-cost sensors to measure fugitive methane emissions. Dr. Moffet is also involved with air quality field study design, instrument selection, quality assurance documentation, and field operations.

If you have a need related to PFAS testing, email Dr. Moffet at [email protected]