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.1 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, HFC152a, 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.

 

1

See page 17 of Newman et al. (2009). HCFCs and HFCs: An Update from the Scientific Assessment Panel., available from 

http://www.r744.com/files/news/HCFCs-HFCs-An-update-from-the-SAP.pdf
- 1 -

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 HFO1234yf 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)
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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, HFC152a 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 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 
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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 (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/m

3

) 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 B1.2 

EPA has established a Reference Concentration (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 108ppt) for acetaldehyde.

3

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 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)

 

2

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

3

http://www.epa.gov/chemfact/s_acetal.txt
- 4 -

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.
- 5 -

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 (HFO1234yf). 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 chemistry of CF3CFHF2 (HFC152a): Kinetics, Mechanisms, and Products of Cl atom- and OH radical-Initiated Oxidation in the 

Presence and Absence of NO. J. Phys. Chem., A 2005, 109, 9061-9069

Wallington, T.J., Hurley, M.D., Fracheboud, J.M., Orlando, J.J., Tyndall, G.S., Sehested, J., Mogelberg, 

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