Challenges Associated with Atmospheric Transport of PFAS

Per- and polyfluoroalkyl substances (PFAS) are a generic family of consumer product chemicals that are heat, grease, stain, and water resistant. Under certain conditions (e.g., industrial stack emissions,  fire suppression, incineration, or combustion), PFAS are emitted into the atmosphere and can be transported globally, as shown in Figure 1.

There are various challenges related to quantifying airborne PFAS, including identifying emission sources, adequately performing complex PFAS test methods while avoiding contamination, as well as understanding atmospheric transformation and deposition. Let’s briefly discuss how to evaluate air emissions as a potential health concern.

Identifying Emissions Source

The extent of atmospheric fate and transport depends on the factors related to the PFAS emission source and topography, including:

• How tall is the emission source? Is it a ground level fire suppression system or an industrial stack emission hundreds of feet above ground?
• What is the temperature of the emission source? Manufacturing processes that bake PFAS onto consumer products result in warmer emissions that will tend to rise in the atmosphere vs. ground level fire suppression system.
• What type of PFAS are emitted into the atmosphere? PFAS vapors are mostly neutral fluorotelomer alcohols (FTOHs), which tend to make up most PFAS present in the atmosphere over urban areas, open oceans, and remote areas. PFAS particles are also emitted into the atmosphere (e.g., perfluorooctanoic acid (PFOA) sorbs to smaller particles; perfluorooctane sulfonic acid (PFOS) sorbs to larger particles); however, they make up a much smaller portion of atmospheric PFAS.
• What kind of topography is near the emission source? PFAS tend to travel further where the topography is flat (no hills or mountains to cause PFAS deposition).

Figure 1: PFAS Conceptual Site Model for Industrial Emission Sources.

Source: June 2022’s ITRC PFAS Guidance, § 9: Site Risk Assessment, Fig 9-2. Credit: L Trozzolo, TRC

Atmospheric Transformation of PFAS

While in the atmosphere, the transformation of neutral FTOH into perfluoroalkyl carboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs), such as PFOA, perfluorononanoic acid (PFNA) and PFOS occurs through exposure to sunlight and oxygen, which can take place over days to weeks. The long atmospheric residence time of FTOH allows for long-range transport (LRT) of FTOH and its transformed products to remote areas, including the Arctic and Antarctic.

Atmospheric Deposition – What Goes Up, Must Come Down

Deposition of PFAS occurs by either wet deposition through precipitation or dry deposition. Deposition occurs over a period of a few days (for particulates) to a few weeks (for vapors).

Regulating Air Emissions

Now that we understand atmospheric fate and transport of PFAS, how are air emissions currently regulated?

• November 30, 2023: The 189 currently listed PFAS are no longer eligible for de minimis exemption related to Toxic Release Inventory (TRI) reporting.
• August 2023: The Federal Register proposal plans to update the Air Emissions Reporting Requirements (AERR) to mandate the collection of certain additional emissions data critical to conducting analyses related to air quality, risk assessment, and various regulatory and non-regulatory activities.

The Environmental Protection Agency (EPA) is in the process of categorizing PFAS as Hazardous Air Pollutants (HAPs) through the Protect Act of 2022. This house bill mandates the EPA to designate all PFAS as HAPs under the Clean Air Act.

Evolving PFAS Air (Stack) Emission Sampling and Analysis Methods

Air emissions are sampled and analyzed using Other Test Methods (OTMs). First documented in 2021 (USEPA, 2021), OTM-45 is the first PFAS air emissions test method for stationary source air emissions. This method can analyze 50 semi-volatile and non-volatile compounds in gaseous and particulate-bound media. Currently, OTM-45 cannot measure non-polar PFAS; however, method modifications to capture non-polar species are occurring. OTM-50 is currently under development for non-polar volatile PFAS compounds using whole air canisters, and OTM-55 is under development for non-polar, semi-volatile and non-volatile PFAS compounds, including FTOHs and products of incomplete combustion or destruction (PICs or PIDs).

OTM-45 is not subject to federal rulemaking, but is EPA-reviewed and EPA-verified, which provides regulatory agencies and the public with a dependable analytical method at the moment. EPA announced that revisions will continue for all OTMs, ensuring PFAS air emission sampling and analysis methods will improve and evolve.

Next Steps

The presence of PFAS in air poses multiple challenges regarding source identification, analytical methods and how to manage air emissions as a potential health concern. These challenges highlight the need for airborne risk-based guidance, establishing air screening levels and inhalation toxicity information (inhalation toxicity values are currently not available). While the introduction of the Other Test Method (OTM-45) marks a crucial step in quantifying PFAS air emissions for polar PFAS, ongoing modifications and development of OTM-50 and OTM-55 will expand air/emission analysis to non-polar PFAS.

One day soon, we will be able to quantify human health and ecological concerns associated with air emissions and atmospheric transport of PFAS. With more than 200 air quality management professionals operating from a network of over 30 offices, TRC is able to support your PFAS emissions measurements and reporting needs.