MEMORANDUM

To:	Margaret Sheppard; U.S. EPA 

Cc	Melissa Fiffer, Monica Shimamura, and Bella Maranion, U.S.EPA

From:	Neha Mukhi, Candace Prusiewicz, Reva Rubenstein, Ed Carr, Emily
Herzog, and Mark Wagner; ICF International 

Date:	July 20, 2010

Re:	Summary of HFO-1234yf Breakdown Products and Impacts of Aldehydes
(Deliverable under EPA Contract Number EP-W-06-008 Task Order 038, Task
01)

 

On December 19, 2009, EPA received a comment on the proposed rule,
Protection of the Stratospheric Ozone: New Substitute in the Motor
Vehicle Air Conditioning Sector under the Significant New Alternatives
Policy (SNAP) Program (EPA-HQ-OAR-2008-0664), stating:

A first analysis based on a slide presentation given at the Montreal
Protocol Geneva meeting in July 2009 by the Scientific Assessment Panel
shows possible reaction processes and suggests that given the high
chemical reactivity of unsaturated HFCs the toxic impact of aldehydes
would be higher than that of carbonic acids. HFOs could thus harm the
human nervous system. At the same time, given that all aldehydes formed
as end products are water-soluble and will be leached from the
atmosphere, the aldehydes formed as end products of HFOs will be
environmental pollutants.

In response to this comment, ICF has reviewed data on the atmospheric
chemistry of HFO-1234yf, HFC-152a, and HFC-134a and their degradation
products. This memorandum summarizes ICF’s analysis of the possible
pathways for atmospheric degradation of HFO-1234yf and the impacts of
the aldehydes produced as degradation products. 

Please contact Mark Wagner at 202-862-1155 with any questions or
comments.ATMOSPHERIC DEGRADATION OF HFO-1234yf

Hydrofluorocarbons, HFC-134a and HFC-152a, and hydrofluoroolefins such
as HFO-1234yf, undergo atmospheric degradation reactions via numerous
pathways including oxidation with chlorine atoms and hydroxyl (OH)
radicals; interaction with OH radicals is the predominant degradation
reaction.  The chemical degradation pathway is complex and includes
numerous radical species and short-lived intermediates. The most
prevalent, stable, and toxicologically relevant to human health
end-products are summarized and discussed here. 

The major atmospheric oxidation product of HFO-1234yf is trifluoroacetyl
fluoride (CF3COF). For chlorine- (Cl) initiated oxidation reactions
CF3COF is formed in approximately 92% of the reactions along with 56% of
the reactions forming formyl chloride (HCOCl), also formed are carbon
monoxide (CO), and peroxy radical reactions with NO to form NO2 (shown
as XO2).  Other products are formed but are not carried in the
assessment as they either become unreactive or are not important to the
final reaction products of interest. The predominant Cl-initiated
degradation products of HFO-1234yf are summarized in Reaction #1
assuming freely available nitrogen (N2) and oxygen (O2). This reaction
pathway is likely to be important in the marine environment where Cl is
found in greater abundance. 

                                                                      N2
+ O2

CF3CF=CH2 + Cl                    CF3COF + HCOCl + CO + XO2 (Reaction
#1)

Hydroxyl mediated oxidation is considered the predominant degradation
pathway of HFO-1234yf (Luecken et al., 2010). CF3COF is formed in nearly
all OH-initiated oxidation degradation of HFO-1234yf  along with
formaldehyde (HCHO) and hydroperoxy radicals (HO2) and peroxy radical
reactions with NO to form NO2 (shown as XO2)  (Hurley et.al., 2007;
Luecken et al., 2010). 

                                                                      N2
+ O2

CF3CF=CH2 + OH                    CF3COF + HCHO + XO2 + HO2 (Reaction
#2)

CF3COF, the predominant atmospheric degradation product of HFO-1234yf,
is hydrolyzed to trifluoroacetic acid (CF3COOH) in the hydrosphere
(Papadimitriou et al., 2008).  Due to the formation of peroxy radicals,
the concentration of ground level ozone will also consequently increase
(Luecken et al., 2010 and Papadimitriou, et al., 2008).  This ground
level ozone reacts with propene in the atmosphere leading to the
formation of acetaldehyde.  Therefore, this secondary effect from the
degradation of HFO-1234yf will lead to a minor increase in the
concentration of acetaldehyde.

ATMOSPHERIC DEGRADATION OF HFC-134a AND HFC-152a

Like HFO-1234yf, the primary degradation pathway of HFC-134a is
initiated with tropospheric hydroxyl radicals.  However, HFC-134a reacts
less readily with OH than HFO-1234yf reacts with OH. The presence of
nitrogen oxides (NOx) in the atmosphere also influences the degradation
products formed from HFC-134a. 

The major atmospheric oxidation products of HFO-134a are carbonyl
fluoride (COF2), CF3COF, formyl fluoride (HCOF), and HCOOH, as depicted
in Reaction #3 (Kotamarthi et al., 1998).  COF2 is rapidly hydrolyzed in
the presence of water to form HF (hydrogen fluoride) and CO2 (carbon
dioxide).  In addition, HCOF decomposes at room temperature to form HF
and CO.   Because the reaction rate of HFC-134a with hydroxyl radicals
is slower than the reaction rate of HFO-1234yf with hydroxyl radicals,
it is estimated that HFC-134a will produce smaller yields of CF3COOH—7
to 21 percent—from the hydrolysis of CF3COF (Wallington et al., 1996).


CF3CH2F  (   COF2 + CF3COF   + HCOF + HCOOH (Reaction #3)

HFC-152a is oxidized in the atmosphere in a similar manner as HFC-134a
and HFO-1234yf. However the major end-product of HFC-152a is chemically
dissimilar.  In the absence of NOx, HFC-152a is oxidized to
predominantly form COF2 for about 97% of the reactions.  In about 3% of
the reactions the presence of NOx, causes both COF2 and CF3COF to be
formed; the concentration of CF3COF increases as the concentration of
available NO increases.  It’s estimated that the bulk (> 75%) of
HFC-152a is atmospherically degraded to form COF2 while approximately 25
% is converted to CF3COF (Taketani et al., 2005).

CH3CHF2 (  COF2 + CF3COF (Reaction #4) 

Table   SEQ Table \* ARABIC  1 : Comparison of Atmospheric Degradation
Products initiated by OH

Compound	HFC-134a	HFC-152a	HFO-1234yf

Formula	CF3CH2F	CH3CHF2	CF3CF=CH2

IUPAC name	1,1,1,2-tetrafluoroethane	1,1-difluoroethane
2,3,3,3-tetrafluoropropene

Atmospheric lifetime	14.4 years	1.4 years	11 days

k (OH  + HFC or HFO)

	3.37 x 10-15 (a)

cm3/molecule. sec	3.08 x 10-14 (b)

cm3/molecule. sec	1.05 x 10-12 exp (-35/T) (c)

cm3/molecule. sec

Major atmospheric oxidation products initiated by OH	CF3COF
(trifluoroacetyl fluoride) 

COF2 (carbonyl fluoride)

HCOF (formyl fluoride)	CF3COF (trifluoroacetyl fluoride)

COF2 (carbonyl fluoride) 

	CF3COF (trifluoroacetyl fluoride) 

HCHO (formaldehyde) 

Hydroperoxyl radical (HO2)

NO2

Further conversion of major atmospheric oxidation products	COF2
converted into CO2 and HF within 1-2 weeks.

CF3COF further hydrolyzed to CF3COOH (trifluoroacetic acid).

HCOF decomposes to HF and CO	COF2 converted into CO2 and HF within 1-2
weeks.

CF3COF further hydrolyzed to CF3COOH (trifluoroacetic acid).	CF3COF
further hydrolyzed to CF3COOH (trifluoroacetic acid).

Sources: (a) Franklin (1993); (b) Taketani et al. (2005); (c)
Papadimitriou, et al. (2008).

ALDEHYDES FROM HFO-1234yf ARE NOT A CONCERN

The primary atmospheric degradation products of HFO-1234yf, HFC-134a,
and HFC-152a are summarized in Table 1.  Although the atmospheric
degradation products of HFO-1234yf, HFC-134a, and HFC-152a are similar
and all include CF3COH, the quantities in which they are produced differ
because HFO-1234yf, an unsaturated hydrofluorocarbon, reacts more
rapidly with OH radicals compared with HFC-134a and HFC-152a, saturated
hydrofluorocarbons. 

The remaining paragraphs provide an overview of the physical and
chemical properties of aldehydes, exposure levels of concern and related
impacts, projected maximum increases in daily average concentrations of
formaldehyde, and a discussion on why aldehydes formed due to
atmospheric degradation of HFO-1234yf are not a concern.

Formaldehyde is an ubiquitous, colorless gas with a pungent, suffocating
odor at room temperature; the odor threshold for formaldehyde is 0.83
ppm (830,000 ppt).  Acetaldehyde is a colorless liquid with an odor
threshold of 0.21 ppm (210,000 ppt).  The major acute and chronic toxic
effects associated with exposures to either aldehyde are eye, nose, and
throat irritation and effects on the nasal cavity.  Other effects seen
from exposure to high levels of formaldehyde in humans are coughing,
wheezing, chest pains, and bronchitis. Animal studies have reported
effects on the nasal respiratory epithelium and lesions in the
respiratory system from chronic inhalation exposure to formaldehyde and
acetaldehyde. 

EPA has not established a Reference Concentration (  HYPERLINK
"http://www.epa.gov/ttn/atw/hlthef/hapglossaryrev.html" \l "rfc"  RfC )
for formaldehyde. However, the Agency for Toxic Substances and Disease
Registry (ATSDR) has established a chronic inhalation minimal risk level
(MRL) of 0.003 ppm (3,000 ppt or 0.004 mg/m3) based on respiratory
effects in humans. The MRL is an estimate of the average daily human
exposure to a hazardous substance that is likely to be without
appreciable risk of adverse non-cancer health effects over a specified
duration of exposure. EPA considers formaldehyde to be a probable human
carcinogen (cancer-causing agent) based on limited evidence in humans
and sufficient evidence in laboratory animals and has ranked it in EPA's
Group B1.  

EPA has established a Reference Concentration (  HYPERLINK
"http://www.epa.gov/ttn/atw/hlthef/hapglossaryrev.html" \l "rfc"  RfC )
of 0.005 ppm (5,000 ppt or 0.009 mg/m3) for acetaldehyde. EPA considers
acetaldehyde as a “probable human carcinogen" and IARC classifies it
as "possibly carcinogenic to humans" based on increased incidences of
nasal tumors in animal studies.  OSHA has established a PEL (8 hr TWA)
of 200 ppm (2 x 108 ppt) for acetaldehyde.  HYPERLINK ""   

Using an extended version of the carbon bond five chemical mechanism as
developed by Luecken et al. (2010) and incorporating the gaseous and
aqueous chemistry of HFO-1234yf and its products, EPA’s CMAQ model
version 4.7 with a 36 x 36-km grid resolution was used to estimate the
difference between the existing daily average concentrations of
formaldehyde and acetaldehyde in Houston and Los Angeles and the
increase in concentrations from the introduction of HFO-1234yf. 
Emission assumptions of HFO-1234yf were based on the worst case scenario
developed for ICF International’s Assessment of the Potential Impacts
of HFO-1234yf and the Associated Production of Trifluoroacetic Acid
(TFA) on Aquatic Communities, Soil and Plants, and Local Air Quality
(ICF International 2010).  The model provides the estimated change in
daily average formaldehyde and acetaldehyde concentrations for each grid
cell for both the Los Angeles and Houston regions.  The value from the
grid cell in each region with the greatest increase in concentration can
then be selected.  Based on data for the last day of each month, the
maximum increase in daily average concentrations of formaldehyde and
acetaldehyde for each region are shown in Table 2.

Table   SEQ Table \* ARABIC  2 : Maximum Increase in Daily Average
Concentrations of Formaldehyde and Acetaldehyde (ppt)

Date	Los Angeles	Houston

	Formaldehyde	Acetaldehyde	Formaldehyde	Acetaldehyde

Jan 31	1.96	0.07	0.09	0.01

Feb 28	0.41	0.01	0.03	0.05

Mar 31	4.42	0.47	0.14	0.02

Apr 30	8.64	0.36	0.44	0.04

May 31	7.02	1.15	0.13	0.02

Jun 30	3.39	0.23	0.30	0.03

Jul 31	2.40	0.09	0.25	0.03

Aug 31	1.51	0.10	0.09	0.01

Sep 30	6.06	0.24	0.22	0.02

Oct 31	0.57	0.01	0.17	0.01

Nov 30	0.30	0.02	0.06	<0.01

Dec 31	0.89	0.02	0.04	0.01

Average	3.13	0.23	0.16	0.02

Source: CMAQ model version 4.7 using chemistry developed by Luecken et
al. (2010)

It can be conservatively assumed that the average of the maximum daily
values on the last day of the month (see Table 2), for each modeled
region, provides an upper bound estimate of the annual average
concentration increase for formaldehyde and acetaldehyde.  As such, for
Los Angeles and Houston, the formaldehyde concentration is expected to
increase on average by no more than 3.13 ppt and 0.16 ppt, respectively.
This increase is comparable to the estimated maximum annual average
increase in formaldehyde concentrations of 1.1 ppt. reported by Kajihara
et al. (2010) for the Kanto plain region in Japan from the atmospheric
degradation of HFO-1234yf.  Further, these annual average increases are
well below the current annual average formaldehyde concentration for the
United States, as determined at the county level across the US by the
National Air Toxic Assessment (2002), where annual average formaldehyde
concentrations range between 80 ppt (pristine) to 3,300 ppt (New York,
New York).  

The National Air Toxic Assessment (2002) also determined the county
level annual concentration for acetaldehyde, which ranges from 47 ppt to
3,100 ppt.  This annual concentration is approximately three orders of
magnitude higher than the projected annual average increase in
acetaldehyde concentration for Los Angeles (0.23 ppt). 

Thus, changes in ambient formaldehyde and acetaldehyde concentrations
from the introduction of HFO-1234yf would be well below current
background concentrations even in pristine environments.  Finally,
projected increases in formaldehyde concentrations in LA and Houston
represent less than 0.1% and 0.005% of the MRL threshold concentration
for formaldehyde while the projected increases in acetaldehyde
concentrations are less than 0.005% of the RfC.  As a result, increases
in formaldehyde and acetaldehyde concentrations due to emissions of
HFO-1234yf are not expected to have an adverse effect on human health or
the environment.

REFERENCES

Franklin J.  1993. The atmospheric degradation and impact of
1,1,1,2-tetrafluoroethane (Hydrofluorocarbon 134a). Chemosphere 27(8): 
1565-1601.

Hurley, MD, Wallington, TJ, Javadi, MS, and Nielsen, OJ. Atmospheric
chemistry of CF3CF=CH2: Products and mechanisms of Cl atom and OH
radical initiated oxidation. Chemical Physics Letters 450 (2008),
263-267

ICF International. 2010. Assessment of the Potential Impacts of
HFO-1234yf and the Associated Production of Trifluoroacetic Acid (TFA)
on Aquatic Communities, Plants and Soils, and Local Air Quality.
Prepared by ICF International for U.S. EPA. May 25, 2010.  

Kajihara, Hideo, Kazuya Inoue, Kikuo Yoshida, and Ryuichi Nagaosa. 
Estimation of environmental concentrations and deposition fluxes of
R-1234-YF and its decomposition products emitted from air conditioning
equipment to atmosphere  Presented at the 2010 International Symposium
on Next generation Air Conditioning and Refrigeration Technology, 17 –
19 February 2010, Tokyo, Japan.

Kotamarthi, V.R., Rodriguez, J.M., Ko, M.K.W., Tromp, T.K., Sze, N.D.,
and Prather, M.J. Trifluoracetic acid from degradation of HCFCs and
HFXs: A three-dimensional modeling study. Journal of Geophysical
Research, Vol. 103, No. D5, 5747-5758- March 20, 1998

Luecken, D.J., Waterland, R.L., Papasavva, S., Taddonio, K.N., Hutzell,
W.T., Rugh, J.P., and Anderson, S.O. Ozone and TFA Impacts in North
America from Degradration of 2,3,3,3-Tetrafluoropropene (HFO-1234yf). A
Potential Greenhouse Gas Replacement. Environ. Sci. Technol., 2010, 44
(1), pp 343–348

National Air Toxic Assessment. 2002. Available online at
http://www.epa.gov/ttn/atw/nata2002/tables.html.

Papadimitriou, V. C.; Talukdar, R. K.; Portmann, R. W.; Ravishankara, A.
R.; Burkholder, J. B. CF3CF=CH2 and (Z)-CF3CF+CHF: temperature dependent
OH rate coefficients and global warming potentials. Phys. Chem. Chem.
Phys., 2008, 10(6):808–820.

Taketani, F, Nakayama, T., Takahashi, K., and Matsumi, Y. Atmospheric
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Wallington, T.J., Hurley, M.D., Fracheboud, J.M., Orlando, J.J.,
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excited CF3CFHO radicals in the atmospheric chemistry of HFC-134a. J.
Phys. Chem, 1996, 100(46) 18116-18112

 See page 17 of Newman et al. (2009). HCFCs and HFCs: An Update from the
Scientific Assessment Panel., available from   HYPERLINK
"http://www.r744.com/files/news/HCFCs-HFCs-An-update-from-the-SAP.pdf" 
http://www.r744.com/files/news/HCFCs-HFCs-An-update-from-the-SAP.pdf  

   HYPERLINK "http://www.epa.gov/ttn/atw/hlthef/formalde.html" 
http://www.epa.gov/ttn/atw/hlthef/formalde.html 

   HYPERLINK "http://www.epa.gov/chemfact/s_acetal.txt" 
http://www.epa.gov/chemfact/s_acetal.txt  

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