1. HFCs and Their Final Fate Becky Otter Chemistry 481 February 3, 2005

2. What are HFCs?  HFCs or hydrofluorocarbons are made of H,F, & C  They are used as replacements for chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs)

3. HFCs  1,1,1,2-tetrafluoroethane or HFC-134a  HFCs are used as replacements because have near- zero ozone depletion potentials (ODP), short atmospheric lifetimes, less or non-flammable, low global warming potentials (GWPs), are cheap, high volatility, and very low solubility in water.  Most importantly the C-H bonds allow the HFCs to react with OH radicals and breakdown (Tsai, Chemosphere 61, 2005 p1539-1547) HFC-134a CH2FCF3

4. Oxidation of HFC-134a Pathway 1 Pathway 2 TFA HFC134-a CF 3 CFHO radical CF 3 COF CF3CFHO radical CF3COF CF 3 radical

5. What happens to HFCs after they are released into the environment?  HFCs remain in the lower atmosphere  There are several products of oxidation: TFA, HF, C 3 FOF, CO 2, CF 3 OH, HCOF  Some HFCs (HFC-32, HFC- 143a, & HFC-152a) can form flammable mixtures with air  Burning these compounds produces more toxic compounds and other GHGs adding to the Greenhouse Effect (Tsai, Chemosphere 61, 2005 p1539-1547)

6. HFCs Atmospheric lifetime (year) GWPa Flammability (%) log Kowd LFLbUFLc HFC-2326012 000None0.58 (0.64) HFC-32555012.7–33.50.71 (0.21) HFC-125293400None0.84 (1.48) HFC-1349.61100None0.94 HFC-134a13.81300None0.98 (1.06) HFC-143a5243007.0–19.01.03 HFC-152a1.41204.2–20.21.13 (0.75) HFC-227ea333500None1.1 HFC-236ea101200None1.2 HFC-236fa2209400None1.24 HFC-245ca5.96407.0–14.41.33 HFC-245fa7.2950None1.33 (1.35) HFC-365mfc9.98903.8–13.31.79 (1.61) HFC-43-10mee151500None1.72 (Tsai, Chemosphere 61, 2005 p1539-1547)

7. So What Does This Mean?  Since HFCs have very low solubility in water they do not stay in water very long thus not serving a large risk  COF 2 is a irritating gas and can be hydrolyzed to HF which is moderately toxic to humans, however there isn’t information on the atmospheric concentration on the degradation product.  TFA is also a skin/tissue irritant because it is a strong carboxylic acid-it can be acutely toxic to the biosystem

8. And Time Says?  Culbertson and associates wanted to see how the relative amounts of CF 3 containing compounds in background air were changing over the past two decades  The HFCs in question where CF 3 H (HFC-23), CF 3 CH 3 (HFC- 143a), and CF 3 CH 2 F (HFC-134a) Palmer Station, Antarctica Cape Meares, OR Point Barrow, AK

9. Table 1: Annual Average concentrations of CF 3 - containing trace gases in parts per trillion by volume ( Culbertson, et al Chemosphere 55, 2004 pg 1109-1119)

10. Fig. 4. OR emissions ( Culbertson, et al Chemosphere 55, 2004 pg 1109-1119) Fig. 5. AK and Antarctica emissions Take home message: There has been a increase in the concentration of HFC in the atmosphere in OR, but only a slight difference has been seen in AK and Antarctica= Shows difference in where the emissions are coming from

11. Table 2. Average calculated emissions in Greenhouse Gases yr−1 over five-year periods ( Culbertson, et al Chemosphere 55, 2004 pg 1109-1119)

12. What they concluded:  That over the past 2 decades, the emission rates have increased thus the concentration of HFCs has increased  There is a difference seen between the two hemispheres most likely due to the fact that the Northern hemisphere emits more HFCs

13. CONCLUSIONS  HFCs are in fact GHGs however I believe they have much less environmental impacts than CFCs and HCFCs  The products of oxidation are “rained out” and the atmospheric lifetime is relatively short for most HFCs-posing a much smaller environment impact than the alternatives  From experiments measuring concentrations of HFCs, there is an increase in the emission rates