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Case Study

Assessment of a New Car Refrigerant in Stagnant Surface Waters

We were tasked to help a client with an assessment of a new car refrigerant in stagnant surface waters. In 2012 a next-generation mobile air-conditioning (MAC) refrigerant, HFO-1234yf (CF3CF¼CH2, CAS 754-12-1), was introduced as a replacement for the current refrigerant, HFC-134a.  This new refrigerant, when exposed to moisture in the air, breaks down to TFAA which can accumulate in terminal waterbodies. The challenge was to determine at the continent scale where terminals (stagnant waterbodies) occur and what the accumulation rate of TFAA would be.

Our Findings

The current generation automobile air-conditioning refrigerant, HFO-1234yf, replaced HFC-134a in 2012. In the atmosphere, it ultimately forms trifluoroacetic acid (TFA(A); CF3COOH), which is subsequently scavenged by precipitation and deposited on land and water as trifluoroacetate (TFA). Trifluoroacetate is environmentally stable and has the potential to accumulate in terminal water bodies, that is, aquatic systems receiving inflow with little or no outflow and with high rates of evaporation. In this study atmospheric modeling and geographic information systems (GIS) were used to assess the concentrations of TFA in surface water bodies over extended periods. Simplistic GIS first-order accumulation models were developed to estimate surface water concentrations based on areal deposition. Specifically terminal and non-flowing waterbodies are of interest, because of continued accumulation of TFA. A challenge was to determine which waterbodies in the contiguous US were considered terminal. A few examples include Mono Lake (CA) and the Great Salt Lakes (UT). Concentrations of TFA in terminal water bodies across North America are estimated to range between current background 1 to 6 mg/L after 10 years of accumulation and increase to 1 to 15 mg/L within a 50 year period. In extreme cases concentrations of up to 50 to 200 mg/L were calculated in arid regions of the US, such as the Sonoran Desert along the California/Arizona border.

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