Deposition and rainwater concentrations of trifluoroacetic acid in the United States from the use of HFO‐1234yf

Abstract

Currently, HFC‐134a (1,1,1,2‐tetrafluoroethane) is the most common refrigerant in automobile air conditioners. This high global warming potential substance (100 year GWP of 1370) will likely be phased out and replaced with HFO‐1234yf (2,3,3,3‐tetrafluoropropene) that has a 100 year GWP of 4. HFO‐1234yf will be oxidized to produce trifluoroacetic acid (TFA) in clouds. TFA, a mildly toxic substance with detrimental effects on some aquatic organisms at high concentrations (≥100μgL−1), would be transported by rain to the surface and enter bodies of water. We investigated the dry and wet deposition of TFA from HFO‐1234yf over the contiguous USA using the Advanced Research Weather Research and Forecasting model (ARW) with interactive chemical, aerosol, and cloud processes (WRF/Chem) model. Special focus was placed on emissions from three continental USA regions with different meteorological characteristics. WRF/Chem simulated meteorology, cloud processes, gas and aqueous phase chemistry, and dry and wet deposition between May and September 2006. The model reproduced well the multimonth total sulfate wet deposition (4% bias) and its spatial variability (r = 0.86) observed by the National Atmospheric Deposition Program. HFO‐1234yf emissions were obtained by assuming the number of automobile air conditioners to remain unchanged, and substituting HFO‐1234yf, mole‐per‐mole for HFC‐134a. Our estimates of current HFC‐134a emissions were in agreement with field data. Average TFA rainwater concentration was 0.89μgL−1, with peak values of 7.8μgL−1, for the May–September 2006 period over the contiguous USA. TFA rainwater concentrations over the dry western USA were often significantly higher, but wet‐deposited TFA amounts remained relatively low at such locations.

Evidence for the Formation of Difluoroacetic Acid in Chlorofluorocarbon-Contaminated Ground Water

“…Table 1 reveals the concentrations of TFA and DFA in rainwater collected with a temporal interval of 24 h. Assuming a depuration effect by the first rainfall after a longer dry period, the TFA concentration decreased in the consecutive rainfall. This TFA concentration range resembled the average concentration levels observed in the USA [13]. The TFA:DFA ratio of about 10:1 in both rainwater samples correlates well with the airborne TFA:DFA ratio reported for urban areas in Ontario, Canada [7].…”

Challenges in the analytical determination of ultra-short-chain perfluoroalkyl acids and implications for environmental and human health

“…A proposed replacement is HFO-1234yf (2,3,3,3tetrafluoropropene), which has a shorter lifetime and higher conversion rate into TFA compared with HFC-134a. A few studies have estimated that concentrations of TFA in air and wet deposition will increase in the future assuming a complete shift to HFO-1234yf [60][61][62]. Results indicate that the TFA concentration in air will increase with at least a factor of 10 in some European areas [60].…”

Temperature‐Dependence of the Rates of Reaction of Trifluoroacetic Acid with Criegee Intermediates

“…They react only slowly with hydroxyl radicals and do not photolyse at actinic wavelengths . Current atmospheric models therefore incorporate surface deposition and rain‐out as their main loss processes . However, recent evidence from laboratory studies indicates that organic acids, and other trace atmospheric molecules, react with Criegee intermediates with room‐temperature rate coefficients that approach (or exceed) the expected gas‐kinetic limits predicted by collision rates .…”