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

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

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 p ) HFC-134a CH2FCF3

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

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 p )

HFCs Atmospheric lifetime (year) GWPa Flammability (%) log Kowd LFLbUFLc HFC None0.58 (0.64) HFC – (0.21) HFC None0.84 (1.48) HFC None0.94 HFC-134a None0.98 (1.06) HFC-143a – HFC-152a – (0.75) HFC-227ea333500None1.1 HFC-236ea101200None1.2 HFC-236fa None1.24 HFC-245ca – HFC-245fa7.2950None1.33 (1.35) HFC-365mfc – (1.61) HFC-43-10mee151500None1.72 (Tsai, Chemosphere 61, 2005 p )

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

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

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

Fig. 4. OR emissions ( Culbertson, et al Chemosphere 55, 2004 pg ) 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

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

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

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