PFAS atmospheric dispersion, transformation and deposition model

In 2010, Dupont asked Ramboll to support their efforts to advance the science of PFAS transport and better understand its relative contribution to PFAS detected in the environment.

Considering chemical reactions in the atmosphere

Chemical reactions in the atmosphere can produce certain per- and polyfluoroalkyl substances (PFAS), depending on local atmospheric conditions. For example, the gas-phase reaction of fluorotelomer alcohols to form perfluorooctanoic acid (PFOA) and perfluorononanoic acid (PFNA) is known to be sensitive to local concentrations of nitrogen oxides (NOx) in air, which tend to be higher in areas of high population density.

Considering such reactions can be critical to understanding the sources, transport and distribution of PFAS detected in the environment.

Model to evaluate long-range transport of PFAS and PFAS precursors

[Our role] Ramboll developed an atmospheric dispersion, transformation and deposition model with high spatial and temporal resolution to evaluate the long-range transport of PFAS and PFAS precursors. This model is capable of distinguishing spatial regions with high and low concentrations of NOx, especially across areas with many large NOx point sources such as the Eastern United States.

Ramboll's three-dimensional model covered continental North America with a 72 x 72 kilometer grid and one hour temporal resolution to explicitly model direct transport of and surface deposition of several PFAS and PFAS precursors across North America and the North American Arctic.

Results of the modeling were used to identify and assess the impact of potential sources of PFAS detected in air and in rainfall across North America, and resulting PFAS concentrations in soil, surface water, groundwater and wildlife.

Prioritizing efforts to reduce PFAS in air and rainfall

Ramboll’s evaluation assisted in identifying the primary sources of PFAS concentrations reported in air and rainfall across North America, allowing for prioritization of efforts to reduce PFAS levels in the environment.

Ramboll’s work was reviewed by independent experts in the field of atmospheric transport and summarized in an article published in the peer-reviewed journal Environmental Science & Technology.