MEMORANDUM

To: Margaret Sheppard , U.S. EPA

CC: Karen Thundiyil and Monica Shimamura, U.S EPA

From: Emily Herzog, Ed Carr, Kara Altshuler, Toby Krasney, Marian Van Pelt, Mark Wagner, ICF 

International 

Date: August 4, 2009

Re: Revised Final Draft Assessment of the Potential Impacts of HFO-1234yf and the Associated 

Production of TFA on Aquatic Communities and Local Air Quality (Deliverable under EPA 

Contract Number EP-W-06-008 Task Order 026, Task 06)

Please find attached a revised final draft of a paper that examines the emissions of HFO-1234yf and the 

associated production of TFA under several scenarios. The assessment has been revised based on updates 

made to the Vintaging Model assumptions for MVAC end uses. Specifically, the updates include smaller 

charge sizes and a reduction in future market growth rates. While market penetration of the substitute is 

assumed to be the same as in the previous set of assumptions, the growth of the overall sector is assumed 

to be less than the annual 2.6 percent growth rate previously assumed. The revised charge size and 

growth rate assumptions have resulted in a reduction of projected future emissions of HFO-1234yf. 

Please contact Mark Wagner at 202-862-1155 with any questions or comments.
Revised Draft Assessment of the Potential Impacts of 

HFO-1234yf and the Associated Production of TFA on 

Aquatic Communities and Local Air Quality

Prepared for:

Stratospheric Protection Division

Office of Atmospheric Programs

U.S. Environmental Protection Division

1310 L Street, NW

Washington, DC 20005

Prepared by:

ICF International 

1725 Eye Street, NW, Suite 1000

Washington, DC 20006

July 31, 2009
 TFA Assessment

1

 100-year GWPs of Selected HCFCs and HFCs 

Gas

IPCC Second 

Assessment 

Report (SAR)

IPCC Fourth 

Assessment 

Report (AR4)

HCFC-22 1,500 1,810

HCFC-123 90 77

HCFC-124 470 609

HCFC-141b 600 725

HCFC-142b 1800 2,310

HFC-23 11,700 14,800

HFC-32 650 675

HFC-125 2,800 3,500

HFC-134a 1,300 1,430

HFC-143a 3,800 4,470

HFC-152a 140 124

HFC-227ea 2,900 3,220

HFC-236fa 6,300 9,810

HFC-245fa NA 1,030

HFC-365mfc 860 794

Source: IPCC (1996), IPCC (2007)

Executive Summary

HFO-1234yf is a chemical under development for use in motor vehicle air conditioning (MVACs) and has 

the potential to be used more broadly in other end use sectors. Although HFO-1234yf has a low global 

warming potential (GWP) and is thus a desirable alternative to commonly used hydrofluorocarbons 

(HFCs), there is concern that use of HFO-1234yf could negatively impact both local air quality and 

aquatic communities. HFO-1234yf has a photochemical ozone creation potential (POCP) that could 

potentially lead to increased levels of ground ozone. Additionally, there is concern associated with the 

atmospheric degradation of HFO-1234yf, which results in the production of trifluoroacetic acid (TFA). 

TFA has the potential to accumulate on soil, on plants, and in aquatic ecosystems over time and to 

impact the supported plant and animal communities. The following paper describes the production and 

fate of TFA, provides an in-depth discussion of the toxicity of TFA, discusses the scenarios developed for 

this analysis, and discusses the potential impacts HFO-1234yf could have on aquatic ecosystems, soil, 

plants, and local air quality. 

The scenarios developed for this analysis project HFO-1234yf emissions and subsequent production of 

TFA up to 2050 based on market penetrations in the domestic market. In conjunction with three 

dimensional air quality modeling conducted using EPA’s Community Multiscale Air Quality (CMAQ) 

model (CMAQ - Byun, D. W., and J. K. S. Ching. 1999) these projections were used to estimate the 

maximum potential concentration of TFA in rainwater. These projections were also localized and used 

to predict the potential increase in ground level ozone. From this analysis, it was concluded that the 

projected maximum concentration of TFA in rainwater should not result in a significant risk of 

ecotoxicity and that non-attainment resulting from 

HFO-1234yf emissions is unlikely to be a major 

concern for local air quality in most locations.

1. Introduction 

Since the inception of the Significant New 

Alternatives Policy (SNAP) program, a large number of 

substitutes have been reviewed in support of the 

development and commercialization of viable 

replacements for ozone depleting substances (ODS) 

across all of the end use sectors that have 

traditionally used ODS. Approved substitutes have 

included hydrochlorofluorocarbons (HCFCs), 

hydrofluorocarbons (HFCs), blends, hydrocarbons, 

and not-in-kind alternatives. The HFCs have been a 

significant alternative for many sectors because of 

their non-ozone depleting nature, but due to the high 

global warming potential (GWPs) of HFCs, new lowGWP alternatives are being developed. In particular, 

HFO-1234yf is a chemical under development for use 

in motor vehicle air conditioning (MVACs) and has the 

potential to be used more broadly in the 

refrigeration/air conditioning end use sectors. 
 TFA Assessment

2

Sources of TFA

Species Global TFA 

Production (t yr-1)

Halothane 520

Isoflurane 280

HCFC-123 266

HCFC-124 4440

HFC-134a 4560

Fluoropolymers 200

TFA (lab use etc) Negligible

Total 10,266

Source: IPCC/TEAP 2005

HFO-1234yf is proposed to replace HFC-134a in MVACs and has a particularly low GWP of 4.4 compared 

to the HFCs and HCFCs currently in use (as shown in the text box above), HFO-1234yf has the potential 

to significantly reduce the climate impacts of MVACs as well as that of other sectors (Papadimitriou et 

al. 2007).

Although the use of HFO-1234yf could potentially mitigate greenhouse gas emissions, it could also 

potentially contribute to increased levels of ground level ozone. The photochemical ozone creation 

potential (POCP) of HFO-1234yf is dependent on regional conditions and is expected to be similar to that 

of ethylene (Papadimitriou et al. 2007). This POCP value is significantly higher than that of HFC-134a, 

which is nearly zero, and therefore HFO-1234yf may pose a risk to local air quality, if emitted in 

sufficient quantities.

There is additional concern associated with the atmospheric 

degradation of HFO-1234yf which results in the production of 

trifluoroacetic acid (TFA). TFA is a well-known environmental 

contaminant that results from the degradation of halothane (an 

anesthetic introduced clinically in 1956), isoflurane, and 

fluoropolymers as well as HFC-134a, HCFC-123, and HCFC-124. 

In its 2006 report on Environmental Effects of Ozone Depletion 

and Its Interactions with Climate Change, the United National 

Environment Programme (UNEP) stated that risks to humans 

and the environment from TFA and other degradation products 

of HCFCs and HFCs “are considered minimal.” HFO-1234yf was 

not considered in the basket of HFCs at the time that UNEP 

prepared its 2006 report. 

At the current rate of production from atmospheric degradation of HFCs and HCFCs, the level of TFA is 

projected to reach close to 0.0001 mg/L in 2020 in rainwater, about 1,000 times lower than the lowest 

reported no observed effect concentration of 0.12 mg/L (Berends et al. 1999). However, the rate of 

production of TFA from HFO-1234yf is significantly higher than that associated with HFC-134a. With the 

anticipated use (and associated emissions) of HFO-1234yf, TFA has the potential to accumulate in 

seasonal wetlands, which have both little to no outflow and high evaporation rates (e.g., vernal pools, 

playa lakes), over time and may impact the supported plant and animal communities in those wetlands. 

This paper examines the emissions of HFO-1234yf and the associated production of TFA under several 

scenarios and assesses the potential impacts of HFO-1234yf and TFA on aquatic communities and local 

air quality. The remainder of the document is organized as follows:

 Section 2 describes the production and fate of TFA;

 Section 3 provides an in-depth discussion of the toxicity of TFA;

 Section 4 discusses the scenarios developed for this analysis and the resulting emissions of HFO1234yf and production of TFA; and

 Section 5 discusses the results of this analysis, presents an assessment of the potential impacts 

on aquatic ecosystems and local air quality, and identifies the limitations of the analysis.
 TFA Assessment

3

2. Production and Environmental Fate of Trifluoroacetic acid (TFA)

Trifluoroacetic acid (TFA) is produced during the atmospheric breakdown of many fluorocarbons (e.g., 

CFC replacements), including HFO-1234yf. The process is initiated by the gaseous reaction of these 

fluorocarbons with hydroxyl (OH) radicals, eventually resulting in carbonyl products. These halogenated 

carbonyl compounds remain in the atmosphere for about 5 days before they are encapsulated into 

water droplets and hydrolyzed to TFA (Papadimitriou et al. 2007). 

Due to the re-evaporation of cloud droplets, TFA may also re-evaporate to the gas phase. A small 

portion (at most 5%) of gas phase TFA is estimated to react with OH and be dry-deposited to the earth’s 

surface (Kotamarthi et al. 1998). However, TFA is considered highly soluble and is instead expected to 

reincorporate into cloud and rainwater, eventually being wet-deposited to the oceans and land surfaces

(Kotamarthi et al. 1998). After deposition, TFA enters aquatic environments. 

TFA is a strong acid with a reported pKa range of ~0.25-

0.5; therefore, it is expected to completely ionize at any 

pH that occurs naturally (Boutonnet et al. 1999; HSDB 

2008; Kotamarthi et al. 1998). Due to its high solubility, 

volatilization from aqueous solution is not considered to 

be a significant transport pathway. In the aqueous 

phase, TFA does not absorb light at wavelengths greater 

than 250-290 nm (Boutonnet et al. 1999; HSDB 2008), 

thus excluding photolysis as a degradation pathway. 

There are few studies available that provide information 

on the movement of TFA in solid and liquid media. 

Based on a low Henry’s Law constant and a low Kow (noctanol/water partition coefficient) (Franklin 1993), it 

has been predicted that TFA would partition 

predominantly in water (Bowden et al. 1996; 1998). 

However, studies of TFA adsorption in soils have been performed in both upland forest and forest 

wetland environments in the Hubbard Brook Experimental Forest in New Hampshire, with varying 

results (Likens et al. 1997; Richey et al. 1997). These studies indicate that TFA is measurably retained in 

soils in those environments, with wetland systems retaining more applied TFA than the forest system. 

For example, within 1-3 weeks, applied TFA moved through the forest soil profile with drainage water, 

and more than 70% of the TFA exited the upland forest in drainage water. The authors suggested that 

TFA would likely be leached from the soil and enter drainage waters { over approximately 2 years until 

the TFA concentrations returned to pre-application levels. In the case of the forest wetland, TFA did not 

move readily with water, and <5% of the applied TFA moved out of the wetland in drainage water. 

Interestingly, the authors did not see an increased concentration of TFA in drainage waters following dry 

spells and the drying of the wetland, indicating that the compound was not concentrating due to 

evaporation. The authors interpreted these data to indicate the compound was being retained in the 

vegetation (20-50%) and forest wetland soils (20-60%). 

A separate study done by the researchers investigated the properties of soils that affect TFA retention 

(Richey et al. 1997). The data indicate that soils with greater amounts of organic matter preferentially 

Chemical and Physical Properties of TFA

Molecular Formula CF3C(O)OH

Molecular Weight 114.02

Vapor Pressure 1.10 x 102mm Hg

Boiling Point 72.4  ̊C

Melting Point -15.4  ̊C

Log Kow 0.50

pKa 0.25-0.5

Koc 3

Henry’s Law Constant 1.11 x 10-7 atm-m3/mol

Solubility Miscible in water at 20  ̊C

Source: Hazardous Substance Data Bank
 TFA Assessment

4

retain TFA compared to well-drained, aerobic soils, with organic soils from wetlands, peatlands, and a 

boreal forest showing the greatest retention of the compound. Further, TFA was retained to a greater 

extent in lower pH environments, but was not retained in the presence of high concentrations of 

fluoride, chloride, and sulfate ions. As mentioned before, TFA is a strong acid; these data suggest that 

soils impacted by acid rain may be further impacted by the deposition of TFA, because of its acidity, 

although the presence of SO4

-

(currently a primary component of acid rain) in large quantities will inhibit 

TFA retention. Studies evaluating effects of TFA deposition/adsorption on soil or sediment chemistry 

have not been identified. Effects of TFA on soil microbial communities are described below.

Studies show that TFA is extremely persistent in aquatic environments. The estimated half-life for 

degradation of TFA in typical environmental conditions via reaction with hydroxyl radicals in water 

would be  100 years (Ellis et al. 2001). Further, data provided by Alternative Fluorocarbons 

Environmental Acceptability Study (AFEAS) member companies indicates that TFA is resistant to 

biodegradation (Franklin 1993).

3. Toxicity of Trifluoroacetic Acid (TFA)

3.1. Aquatic and Environmental Toxicity1

TFA is mildly toxic to plant life (i.e., phytotoxic). In certain environmental conditions, TFA could reach 

concentrations in the future that may be toxic to surrounding plant life. For example, studies show that 

as seasonal wetlands evaporate, the remaining TFA is concentrated; TFA in these standing pools can be 

retained for years, adding to long-term accumulation of TFA in wetlands (Cahill et al. 2001). Increased 

concentrations of TFA can inhibit growth in the most sensitive plants and may affect the survival of 

endangered and endemic plant species (Cahill et al. 2001). Lower aquatic life forms, such as bacteria, 

small invertebrates, and oligochaete worms, do not accumulate large quantities of TFA, and are not

significantly impacted by the compound (Boutonnet et al. 1999). According to a study on the aquatic 

toxicity of TFA, systems exposed to a concentration of 0.10 mg/L are expected to experience no adverse 

effects (Berends et al. 1999), although many organisms show no toxic effects at much higher 

concentrations of the compound (see Table 1 below). 

Lowest observed effect concentrations (LOEC) and no observed effect concentrations (NOEC), as 

summarized by Boutonnet et al. (1999),2 are shown in Table 1.

 

1 The toxicity of TFA has been evaluated in algae, microbial benthic organisms, fish, and freshwater plants. 

Terrestrial plant, laboratory animal, and human study data are not reviewed in this section.

2 Research sponsored by the Alternative Fluorocarbons Environmental Acceptability Study (AFEAS) and conducted 

by independent scientists at universities, private research organizations, and government laboratories.
 TFA Assessment

5

Table 1: Summary of Studies on the Aquatic Toxicity of Sodium Trifluoroacetate (mg/L)

Aquatic Organisms EC50* LOEC** NOEC***

Selenastrum capricornutum 

(freshwater green alga) 

(new name: Raphidocelis subcapitata)

4.8 

1.5 0.36 0.12 0.15 

Anabaena flos-aquae 

(blue-green alga) 2400 1200 600 

Navicula pelliculosa 

(freshwater diatom) 1200 1200 600 

Skeletonema costatum 

(marine diatom) --- --- 2400 

Chlorella vulgaris

(freshwater green alga) --- --- 1200 

Scenedesmus subspicatus 

(freshwater green alga) --- --- ---

Chlamydomonas reinhardtii

(freshwater green alga) --- --- >120 

Microcystis aeruginosa 

(blue-green alga) --- --- >117 

Phaeodactylum tricornutum 

(marine alga) --- --- >117 

Dunaliella tertiolecta

(marine alga) --- --- >124 

Euglena gracilis 

(freshwater alga) --- --- >112 

Daphnia magna

(crustacea) --- --- 1200 

Brachydanio rerio 

(Zebra fish) --- --- 1200 

Lemna gibba 

(duckweed) --- vegetative growth 1100 600 300 

*EC50 = test concentration resulting in a 50% effect; the table lists EC50 for biomass (adverse effects on growth)

**LOEC = lowest observed effect concentration

***NOEC = no observed effect concentration

Source: Boutonnet et al. 1999

At an exposure level of 1200 mg/L of sodium trifluoroacetate, no effects were seen on either 

Brachydanio rerio (zebra fish) after 96 hours or Daphnia magna (a water flea) after 48 hours (Boutonnet 

et al. 1999). In duckweed, mild negative growth effects were seen on frond and weight increase at the 

same exposure level, while no effects were noted at 300 mg/L. Toxicity tests conducted with 11 species 

of algae (Berends et al. 1999) found that, for ten of these species, the effect concentration for 50% of 

the test organisms (EC50) was greater than 100 mg/L. The lowest threshold for effects was observed for 

the unicellular alga, Selenastrum capricornutum; the no-effect concentration (NOEC) was 0.12 mg/L.

Species of flora and fauna found in vernal pools and other seasonal wetlands vary with geography, and 

are established in unique environmental niches. Plant species tend to be annuals, as perennials are not 

adapted to the seasonality of the rainfall. Of the species listed in Table 1, daphnia magna (crustacean) is 

a common resident of vernal pools. Freshwater fairy shrimp (Branchinecta lynchi) and tadpole shrimp 

(Lepidurus packardi), which are found only in California, are obligate vernal pool species that define 

these wetlands. Neither have been tested in published TFA exposure or toxicity studies to date. These 
 TFA Assessment

6

species are adapted to living in an ecosystem that has varying pH and salinity gradients, but there is 

currently no information regarding what, if any, effects increasing TFA concentrations would have on 

the life cycle of these organisms.

More recent research results are summarized in Table 2. These data were taken from articles relative to 

the toxicity of TFA in fish, aquatic plants, and freshwater benthic microbial communities, and they 

indicate that TFA exhibits low toxicity in these receptors. 

Table 2: Summary of Additional Toxicity Studies of Trifluoroacetate (mg/L)

Aquatic Organisms EC50/LC50 LOEC NOEC

Danio rerio (Zebra fish) 

(Wiegand et al., 2000) ---

1,000 

(low elevation of 

GST activity)

4,000 

(no acute effects)

Myriophyllum sibiricum, Myriophyllum spicatum (aquatic plants) 

(exposure to trichloroacetic acid and TFA mixture for 49 days) 

(Hanson et al., 2002)

--- --- 10 

Lemna gibba, Myriophyllum sibiricum, Myriophyllum spicatum 

(aquatic plants [macrophytes]) 

(Hanson and Solomon, 2004a)

EC50 range:

222.1 - 10,000 

M. sib.: 300 

M. spic.: 100 

L. gibba: 100 

M. sib.: 100

M. spic.: 30 

L. gibba: 30 

Pimephales promelas (Fathead minnow) (Geiger et al., 1988, as 

cited in ECOTOX) 7.79 - 1.28 --- ---

Freshwater benthic microbial communities in stream sediments 

(Bott and Standley, 1998) --- ---

0.00002 to 0.2 (no 

effect on acetate 

metabolism)

*GST = glutathione S-transferases

*EC50 = test concentration resulting in a 50% effect; the table lists EC50 for biomass (adverse effects on growth)

*LC50 = concentration at which 50% of the organisms show an effect (mortality)

*LOEC = lowest observed effect concentration

*NOEC = no observed effect concentration

The combined impact of TFA and other haloacetic acids is not likely to create a significant impact on 

exposed species. Hanson et al. (2002) tested two aquatic plant species with a mixture of trichloroacetic 

acid (TCA) and TFA at concentrations up to 10 mg/L, and observed reversible effects on pigment 

concentrations at the start of the study, but no adverse effects thereafter. The authors conclude that, 

based on the lack of morphological or biochemical effects on these aquatic macrophytes, it is unlikely 

that the TCA/TFA mixture causes toxicity at the currently measured environmental concentrations, 

which they report as 0.01 mg/L. Hanson and Solomon (2004a) tested the toxicity of TFA and other 

haloacetic acids (HAA) in the laboratory with three aquatic plants; mass and root measures, such as root 

number and root length, tended to be the most sensitive indicators of HAA toxicity. The results of this 

study were used in an ecological risk assessment for macrophytes and HAA (Hanson and Solomon, 

2004b). The authors compare the thresholds of toxicity for the species tested to measured 

concentrations of HAAs in the environment from Canada, Europe, and Africa to calculate hazard 

quotients. The Hazard Quotient, as defined by Hanson and coworkers, is the ratio of the highest 

expected environmental concentration of HAA (EEC) and the toxicological benchmark concentration 

(TBC); HQ = EEC/TBC. An HQ of greater than 1 indicates a “potential for toxic effects to occur” while 

those less than 1 essentially indicate no risk (“effects are unlikely”). The calculated hazard quotients are 

extremely low (those for TFA with the three macrophytes were all ≤0.000088 or lower), indicating that 

HAAs do not pose a significant risk to freshwater macrophytes at current environmental concentrations 
 TFA Assessment

7

for both single compound and mixture exposures. The thresholds for toxicity in these calculations 

ranged from 4.1 mg/L to 45.9 mg/L, concentrations which are 400-4500-fold greater than those 

currently detected in the environment (Cahill et al. 2001). Therefore, these data indicate that even in 

the event of increased environmental concentrations of TFA, which might result from increased use of 

HFO-1234yf, the risk to environmental receptors is expected to be small.

The potential for bioconcentration in aquatic organisms is low (HSDB 2008), based on one classification 

scheme (Franke et al. 1994). An estimated BCF of 3 for TFA was calculated in fish, using an estimated log 

Kow of 0.50 (Meylan and Howard 1995) and a regression-derived equation (Meylan et al. 1999). 

Boutonnet et al. (1999) conclude that TFA does not accumulate significantly in lower aquatic life forms 

such as bacteria based on results from Bott and Standley (1994, as cited in Boutonnet et al. 1999) in 

which incorporation of radiolabeled TFA increased over 2.5 years from 0.005% of total counts to 0.024% 

of total counts, and based on low bioconcentration factors (BCF) derived in studies with green algae 

(BCF of approximately 10) and duckweed (BCF of 1.0 to 1.6). 

As seasonal wetlands evaporate, TFA can remain in place and can concentrate over several years, 

resulting in long-term accumulation. This accumulation may be linked to increased concentrations of 

TFA in plants in these wetlands, but studies in animals following long-term exposure to TFA have not 

been done to date. In one study, the highest TFA concentrations in water, which occurred just prior to 

the pools drying up, were in the 0.002 to 0.01 mg/L range. This concentration range is lower than the 

lowest reported NOEC of 0.12 mg/L for a species of freshwater green algae. Plants exposed to high 

aqueous concentrations of TFA within the seasonal pools had elevated TFA concentrations with a 

median concentration of 279 ng/g dry weight in their tissues, as compared to 33 ng/g for species 

growing outside the pools (Cahill et al. 2001). A study of the effects of TFA on vernal pool soil microbial 

and plant communities indicated that, at the test concentrations, TFA will not adversely affect the 

development of soil microbial communities and vernal pool plant species. Microbial respiration was not 

affected by TFA exposures up to 10 mg/L, and microbial degradation of TFA was not observed in soils 

incubated for three months. In addition, no adverse physiological responses were observed in wetland 

plants exposed to 0.1 and 1 mg/L TFA. TFA did accumulate in the foliar tissue of wetland plants as a 

function of root exposure concentration, but the concentrations in foliar tissue leveled off and/or 

declined with time (Benesch et al. 2002). Thus, the test concentration of 1 mg/L is a NOEC for plant 

species in vernal pools.

Studies of stomatal uptake in plants following dry deposition are limited. For TFA that is dry deposited, 

ponderosa pines were shown to take up TFA through their foliage (stomatal uptake) at concentrations of 

0.0015 and 0.01 mg/L for four months (Benesch and Gustin 2002). The study authors prevented misted 

TFA from reaching the roots of the trees to ensure they evaluated only foliar uptake. Although TFA 

concentrations were shown to increase in the pine needles over the course of the study, no visual 

morphological or photosynthetic effects were noted at either concentration. No NOEC values have been 

identified based solely on dry deposition of TFA, or on a combined wet/dry deposition model. 

In conclusion, NOECs from the published literature for the most sensitive species were:

 0.12 mg/L for freshwater green algae

 1200 mg/L for a fish species

 No observed adverse effects at up to 10 mg/L for vernal pool microbial species and up to 1 mg/L 

for vernal pool plant species
 TFA Assessment

8

3.2. Human and Animal Toxicity

TFA has low inhalation toxicity, moderate oral toxicity, and the irritation threshold for humans is 54 ppm 

(Boutonnet et al. 1999). The free acid is considered a strong skin and eye irritant. TFA is not 

significantly metabolized by mammals. The sodium salt of TFA (NaTFA) has a much lower toxicity than 

the free acid and will be the focus of this section, as the free acid is not likely to be present at high 

concentrations in environmental media. Animal studies show that the target organ of TFA and its 

sodium salt is the liver. Single doses of up to 2000 mg/kg NaTFA in male mice resulted in fatty liver 

changes, accompanied by increases in glycogen and vacuolization (Rosenberg and Wahlstrom 1971, as 

cited in Boutonnet et al. 1999). Repeated oral dosing of male rats with NaTFA at up to 150 mg/kg-day 

resulted in significantly increased relative liver weights with decreased liver glycogen content (Stier et al. 

1972, as cited in Boutonnet et al. 1999), and doses of up to 500 mg/kg-day of trifluoroacetate caused 

increased liver cell size with peroxisomal proliferation (Just et al., 1989, as cited in Boutonnet et al.; 

1999). The peroxisomal proliferation is unique to the rat, as this effect was not observed in dosed 

guinea pigs. Single doses of 10 mg/kg (ip) or 25 mg/kg (oral) TFA in male rats resulted in no adverse 

testicular effects. Neither TFA nor its salts have been studied in reproductive or developmental assays; 

TFA was present in the amniotic fluid of halothane-dosed pregnant rats, but no fetal effects were 

observed (Ghantous et al. 1986, as cited in Boutonnet et al. 1999). TFA has also been identified in the 

milk of lactating rats (5-23% following saponification) after the administration of HCFC-123 (Buschmann 

1996, as cited in Boutonnet et al. 1999). TFA has also been reported to be non-mutagenic in bacterial 

studies (Blake et al. 1981 and Waskell 1978, both cited in Boutonnet et al. 1999); studies have not been 

conducted to determine its carcinogenic potential. 
 TFA Assessment

9

4. Assessment of Potential HFO-1234yf Emissions and TFA Production 

This analysis is intended as a screening exercise to develop a reasonable worst-case estimate of HFO1234yf emissions and the associated production of TFA under various use scenarios. The remainder of 

this section describes the assumptions used for this analysis to determine potential emissions of HFO1234yf and the expected resultant production of TFA. A discussion on the limitations of the emission 

projections of HFO-1234yf can be found in section 5.3.1 of this paper.

4.1. Scenarios of HFO-1234yf Market Penetration

For this analysis, two scenarios were developed. These scenarios provide reasonable worst-case 

assumptions for the potential market penetration of HFO-1234yf in the domestic market only. Both 

scenarios assume that HFO-1234yf is used as a drop-in replacement for HFC-134a,3 with a replacement 

ratio of 1:1 HFC-134a to HFO-1234yf.4 

 Scenario 1: HFO-1234yf is used in the United States as a new car refrigerant in the MVAC sector. 

HFO-1234yf begins penetrating the market in 2016 reaching 100 percent market penetration by 

2020, as described in Table 3 below. 

 Scenario 2: HFO-1234yf is used in the United States as a new car refrigerant in MVAC systems, 

refrigeration, and stationary AC systems. Similar to scenario 1, by 2020, HFO-1234yf is used in all 

new MVAC systems. For refrigeration and stationary AC systems, HFO-1234yf enters the market 

in 2010, reaches 30 percent penetration of the market in 2015, and 100 percent by 2020. 

The scenarios are summarized in Table 3 below.

Table 3: Summary of Assumed Penetration of HFO1234yf in Scenarios Used in Analysis

Sectors 2010 2015 2020

Scenario 1

MVACs 0% 0% 100%

Scenario 2

MVACs 0% 0% 100%

Refrigeration 6% 30% 100%

Stationary Air Conditioning 6% 30% 100%

4.2. Estimated Emissions of HFO-1234yf

Using EPA’s Vintaging Model, ICF estimated emissions of HFO-1234yf for both scenarios. These 

estimates are summarized in Table 4. A complete table with estimated annual emissions can be found 

in Annex A. Figure 1 and Figure 2 graphically depict the estimated HFO-1234yf emissions for each 

scenario.

 

3

In all scenarios, HFO-1234yf replaces only pure HFC-134a, not any blends with HFC-134a as a component.

4The ratio of HFC-134a to HFO-1234yf has been estimated at 1:0.9, however a 1:1 ratio was used to provide a 

worst case estimate.
 TFA Assessment

10

Table 4: Summary of Estimated Emissions of HFO-1234yf (MT)*

Scenarios 2020 2030 2040 2050

Scenario 1 6,244 28,327 33,196 36,478

Scenario 2 10,345 42,800 55,349 64,324

* ICF projected emissions of HFO-1234yf using special scenarios designed specifically for this analysis and run on 

the U.S. EPA Vintaging Model, Version VM IO File v4.1 5-19-09. 

Figure 1: Estimated Emissions of HFO-1234yf under Scenario 1 (MT)

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

2010 2015 2020 2025 2030 2035 2040 2045 2050

Year

Emissions (MT)

MVAC
 TFA Assessment

11

Figure 2: Estimated Emissions of HFO-1234yf under Scenario 2, by End-Use Sector (MT)

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

2010 2015 2020 2025 2030 2035 2040 2045 2050

Year

Emissions (MT)

Air Conditioning

Refrigeration

MVAC

4.3. Estimated Production of TFA

The production of TFA from HFO-1234yf emissions was estimated under the assumption that 90 percent 

of HFO-1234yf emissions degrade to TFA. These estimates are summarized in Table 5 below. A 

complete table with estimated annual TFA production can be found in Annex B.

Table 5: Summary of Estimated Production of TFA (MT)

Scenarios 2020 2030 2040 2050

Scenario 1 5,620 25,494 29,877 32,830

Scenario 2 9,311 38,520 49,814 57,892
 TFA Assessment

12

5. Assessment of Potential Impacts of HFO-1234yf and TFA

This section uses the projected emissions of HFO-1234yf under scenario 2 described in section 4 to 

predict a reasonable worst case scenario leading to impacts on aquatic communities, soil and plants, and 

local air quality. For all analyses, emissions of refrigerant due to servicing motor vehicle air conditioning 

systems were expected to be higher during the spring and summer, with up to 80% of emissions due to 

repairs occurring from April through August.5 Furthermore, refrigerant emissions from servicing motor 

vehicle air conditioning systems were estimated at 47% of annual refrigerant emissions from motor 

vehicles.6 As a result, the analysis assumes that 59.5% of annual emissions of HFO-1234yf would occur 

from April through August, with 11.9% of annual emissions occurring during each of those five months. 

The remaining 40.5% of annual emissions was modeled to occur from September through March, with 

5.8% of annual emissions occurring during each of those seven months. This assumption was also 

applied to stationary AC end uses based on the assumption that similar patterns of seasonal emissions 

would be attributable to this end-use.

The analysis and discussion included in this section are described as follows.

 Section 5.1 analyzes impacts on aquatic communities, soil, and plants using localized modeling 

that was undertaken for both the Houston region and the South Coast Air Basin region of the 

United States. These areas were chosen based on the potential presence of vernal pools and 

their susceptibility to high TFA deposition concentrations. 

 Section 5.2 analyzes local air quality impacts using scaling rations based on VOC emission 

increases for both the Houston-Galveston region and the South Coast Air Basin. These areas 

were chosen based on their projected dates for reaching ozone attainment which coincide with 

the large increase in HFO-1234yf emission rates. 

 Section 5.3 discusses the limitations and uncertainties related to the modeling and analysis 

conducted for this assessment.

5.1. Aquatic and Soil Impacts 

The general approach to analyze the potential impacts of HFO-1234yf emissions on water, soil, and 

plants involved modeling emissions of SO2 that were scaled proportionately to the projected emissions 

of HFO-1234yf from scenario 2. For example, if SO2 emissions are ten tons per day in a given location 

and for the same geographical region HFO-1234yf emissions are projected to be one ton per day, then 

the resulting modeled concentration would be reduced by a factor of ten. The assumption that SO2 can 

be scaled proportionately to HFO-1234yf is made based on the understanding that the lifetime cycle for 

SO2 to sulfate conversion and their removal in cloud droplets is similar to that of HFO-1234yf to TFA 

removal in cloud droplets. Further, the conversion of SO2 to sulfate is also a reasonable proxy for the 

conversion of HFO-1234yf to TFA because both processes have atmospheric lifetimes of a few days, 

compared to the much longer atmospheric lifetime of HFC-134a of 14 years. 

In the paper by Papadimitriou et al. (2007) the authors demonstrated that the local lifetime for HFO-

 

5 Hoffpauir, Elvis. 2009. Email to Karen Thundiyil, 10 March.

6 U.S. EPA Vintaging Model, Version VM IO File v4.2 10-07-08
 TFA Assessment

13

1234yf was ~ 6.6 days based on typical concentration levels of OH and Cl in a non-marine environment.

Further, the Cl atom abundance is expected to be higher in the marine boundary layer leading to an 

even shorter lifetime (on the order of a few days) as typical for Los Angeles and Houston. The major 

product from HFO-1234yf degradation is CF3CFO which through hydrolysis in cloud droplets will lead to 

the formation of TFA in ~ 5 days. Emissions of SO2 are converted to the sulfate aerosol within clouds by 

oxidation from ozone and OH- molecules. Once in the form of a sulfate aerosol it is removed by water 

droplets. This process has a typical lifetime on the order of ~ 7 days (Lohmann et al., 1999), but is more 

rapid in urban environments with higher background levels of OH- and ozone. 

Thus, to a first approximation the SO2 to sulfate removal is of a similar time period as the HFO-1234yf to 

TFA removal with a similar removal process (wet deposition). Thus, the conversion of SO2 to sulfate is a 

reasonable proxy for the conversion of HFO-1234yf to TFA because both processes have similar 

atmospheric lifetimes and final removal processes.

EPA’s three-dimensional community multiscale air quality model (CMAQ) was applied using emissions of 

SO2 only from Los Angeles and Houston to determine the dry sulfate deposition and sulfate rainwater 

concentrations for a typical one-year (2001) period using hourly meteorological data.7 The sulfate 

concentrations were then scaled on a emissions molar adjusted basis to estimate the maximum 

potential concentration of TFA in rainwater and dry deposition both on an annual basis, as well as for 

the maximum month downwind deposition for both Houston and Los Angeles. To account for the minor 

difference in lifetime for sulfate and for TFA (3 days vs. 5 days) due to in-cloud removal, a log-log 

adjustment was also made to the output of the model to estimate TFA concentrations in rainwater. 

5.1.1. Wet Deposition

Estimates were made for both the dry deposition pathway, as well as the wet deposition pathway. The 

results of the maximum monthly and annual average TFA concentration in rainwater are presented in 

Table 6 for both Houston and Los Angeles. 

Table 6: Estimated Maximum Annual Average TFA and Monthly Maximum TFA Concentration in Rainwater (mg/L)

Year

HFO-1234yf 

Emissions 

Los Angeles 

(MT/yr)

HFO-1234yf 

Emissions 

Houston 

(MT/yr)

Maximum 

Monthly Average 

Downwind of Los 

Angeles

a

Maximum 

Monthly Average 

Downwind of 

Houstonb

Maximum Annual 

Average 

Downwind of Los 

Angeles

Maximum Annual 

Average 

Downwind of 

Houston

2015 63 16 0.02 0.0001 0.00 0.0001

2020 767 191 0.29 0.0013 0.05 0.0009

2025 1,926 481 0.74 0.0034 0.12 0.0022

2030 3,365 840 1.23 0.0055 0.21 0.0038

2040 4,101 1,023 1.57 0.0071 0.25 0.0046

2050 4,766 1,189 1.80 0.0081 0.29 0.0053

a Maximum concentration occurred in July 

b Maximum concentration occurred in April but July was close to April values

 

7 More information is available on the CMAQ model at http://cmascenter.org/.
 TFA Assessment

14

For the Los Angeles region, modeled concentrations of TFA in rainwater are expected to be highest 

during the month of July due to the relatively high concentration of the hydroxyl (OH) radicals in the 

atmosphere during the summer as well as limited rainfall. The high concentration of OH allows more 

HFO-1234yf to react yielding a higher production rate. In addition, the low rainfall rate limits dilution 

and allows for a higher concentration of TFA in rainwater when it does rain occasionally during the 

summer season in the San Gabriel Mountains to the east of Los Angeles. 

Compared to Los Angeles, the precipitation rates in the Gulf Coast region are expected to be much 

higher and more widely distributed in the summer allowing TFA to be more diluted. Furthermore, the 

availability of OH radical is likely lower in Houston due to more frequent cloud cover. As a result, the 

monthly maximum TFA concentration in Houston, which occurs in April with a slightly lower value 

occurring in July, is lower than Los Angeles. On an annual basis the maximum TFA rainfall concentration 

is also considerably lower in Houston than Los Angeles. 

The potential for accumulation of TFA in aquatic environments is greatest for closed aquatic systems 

over multiple years. These types of closed aquatic systems are predominately found in two regions of 

the United States; the glaciated region of eastern North America, which includes 1) the Great Lakes 

Basin and New England, and 2) California and Nevada. Therefore, the Los Angeles regional assessment 

has the potential for maximum annual TFA impact. 

The highest monthly average TFA concentration in rainwater is estimated to be 1.8 mg/L in 2050 located 

downwind of Los Angeles, while the monthly maximum concentration downwind of Houston is 

estimated to be only 0.008 mg/L. The maximum concentrations in both annual and monthly rainwater 

for Houston are well below the 0.12 mg/L no observed effect concentration (NOEC) reported for the 

most sensitive freshwater green algae species tested to date. However, Los Angeles shows the 

potential for concentrations to exceed the no effect levels for this algae species starting in 2020 for the 

monthly maximum concentration and 2025 for the annual average maximum. If the NOEC levels are 

exceeded, sensitive algae species may suffer decline. Note however, all other plant or microbes 

exhibited no effects for the maximum modeled TFA concentrations for both the monthly and annual 

average concentrations. 

In section 3.1 of this paper, it was concluded that the NOEC is 10 mg/L for vernal pool microbial species 

and 1 mg/L for vernal pool plant species. Thus beginning sometime between 2025 and 2030 the 

potential exists for rainwater concentrations to exceed NOECs in vernal pools near Los Angeles during 

the month of July, which represents the monthly maximum concentration. However, the maximum 

annual average of 0.29 mg/L in rainwater downwind of Los Angeles in 2050 and both the maximum 

annual and monthly averages for Houston remain significantly below the NOECs for all vernal pool 

species. Environmental sinks (e.g., adsorption to soil) may further affect the bioavailability of localized 

TFA concentrations such that they could potentially be below the NOEC for both plants and microbes. 

NOECs were compared to rainwater TFA concentrations because for most water bodies, it is difficult to 

predict what the actual TFA concentration will be. This is because concentrations of environmental 

contaminants in most fresh water bodies fluctuate widely due to varying inputs and outputs to most 

ponds, lakes, and streams. Comparison of NOECs to rainwater concentrations of TFA is actually more 

conservative because TFA is expected to be diluted in most freshwater bodies. The exception to this is 
 TFA Assessment

15

vernal pools and similar seasonal water bodies that have no significant outflow capacity. These are 

discussed in more detail in the next section. 

5.1.2. Dry Deposition

The amount of dry deposition was determined assuming a constant deposition velocity for TFA of 1.15

cm/s based on the average deposition rate of 0.88 cm/s for urban-nights, 2.03 cm/s for urban-days, 1.00 

cm/s for desert-days, and 0.7 cm/s for desert nights (Zhang, L., J. R. Brook, and R. Vet 2003). Table 7

presents the results of the maximum annual and monthly TFA deposition. 

Table 7: Estimated Maximum Annual (nmole/m2//yr) Dry Deposition of TFA and Monthly (nmole/m2

/yr) Maximum Dry 

Deposition 

Year

HFO-1234yf 

Emissions Los 

Angeles(MT/yr)

HFO-1234yf 

Emissions 

Houston 

(MT/yr)

Maximum 

Monthly Average 

Downwind of Los 

Angelesa

Maximum 

Monthly Average 

Downwind of 

Houstonb

Maximum Annual 

Average 

Downwind of Los 

Angels

Maximum Annual 

Average 

Downwind of 

Houston

2015 63 16 1,864 69 454 9

2020 767 191 27,241 1,012 5,537 111

2025 1,926 481 69,250 2,571 13,912 279

2030 3,365 840 114,559 4,254 24,308 488

2040 4,101 1,023 146,107 5,425 29,625 594

2050 4,766 1,189 167,892 6,234 34,429 691

a Maximum concentration occurred in March

b Maximum concentration occurred in July

Results show that the monthly peak dry deposition occurs in March for Los Angeles and in July for 

Houston. In Los Angeles, the results also indicate that the deposition is closer to the source region in 

March. This is likely due to lower wind speeds which yield less dispersion as compared to the summer 

months, although there the difference in the peak monthly average concentration between March and 

May – October is small. 

Dry deposition of TFA is likely more of a concern in central and southern California than is wet 

deposition due to the lower rainfall in the state compared to other geographical areas of the United 

States. A comparison of dry deposition rates modeled for areas downwind of Los Angeles is presented 

in Table 8, along with measured TFA flux rates from two vernal pool systems outside of Sacramento, 

California (Cahill et al. 2001; data taken in 1998 and 1999).

The values above indicate that projected maximum annual average deposition of TFA will be greater 

after 2015 than what has been measured in vernal pools in the last decade in Northern California. We 

would expect measured values in vernal pools in Southern California to be somewhat higher owing to 

the reduced rainfall. These projected deposition levels are consistent with the higher localized 

production of TFA from the use of HFO-1234yf. Future TFA loading in seasonal wetlands are predicted 

to increase with increased use of HFO-1234yf. It is difficult to predict at this point whether the 

increased levels will be harmful to typical obligate species in these wetlands, such as fairy and tadpole 

shrimp.
 TFA Assessment

16

Table 8: Future Year(s) Modeled Dry Deposition of TFAa Downwind of Los Angeles and Comparison to TFA 

Measurements in California Vernal Pools, 1998-1999

Modeled Year Maximum Average Yearly 

Deposition Observed Year Values measured in CA vernal pools

nmole/m2-yr g/m2-yr ng/m2-day g/m2-yr

2015 454 52 1998-1999 134* 48.9

2020 5,537 633 1998-1999 110** 40.2

2025 13,912 1,590 1998-1999 152*** 55.5

2030 24,308 2,778

2040 29,625 3,386

2050 34,429 3,935

a Based on HFO1234yf Scenario 2 emission rates (see section 4.1)

Notes: 

Formula weight of TFA is 114 g/mole.

*Time-weighted average of values measured in Davis, CA Jan 1-May 16, 1998.

**Time-weighted average of values measured in Davis, CA Nov 26, 1998-Apr 2, 1999.

***Time-weighted average of values measured in Yolo Country Grasslands Regional Park, CA Jan 6-May 6, 1999.

Values of g/m2-yr – ng/m2-day * 365 days/1000

5.2. Air Quality Impacts 

Increase in ground level ozone is another potential impact of using HFO-1234yf. The potential for ozone 

creation from the release of HFO-1234yf is expected to be similar to the volatile organic compound 

(VOC) – ethylene (Papadimitriou, V. et al, 2007). This fairly reactive compound VOC is an important 

ozone precursor especially in rich NOx environments where the addition of VOC will act linearly to 

increase ground level ozone. 

The Houston-Galveston region and the South Coast Air Basin in California are areas where high levels of 

ground level ozone have been a continuing and chronic problem. These two regions were examined to 

analyze the potential impacts of using HFO-1234yf on ground level ozone, assuming business as usual 

emissions of NOx and VOC. For Houston, data were taken from the Post-1999 Rate of Progress and 

Attainment Demonstration SIP to predict future emissions of NOx and VOC (Texas Natural Resource 

Commission, 2000) up to the 2019 ozone attainment year based on model simulations during the 

summer ozone season. Data for the South Coast region were taken from the 2007 Air Quality Plan, 

which predicts future emissions of NOx and VOC for attaining the ozone standards for 2017 and 2023 

(South Coast, 2007), again based on modeling during the summer ozone season. 

Data for future year projections after 2023 for both Houston-Galveston and the South Coast were 

estimated based on a need for continued reduction in emissions due to increased temperatures from 

global warming. Climate change impacts reported in the IPCC’s 4th Assessment Report (IPCC, 2007)

predict that by 2050 global warming will increase average daily ozone levels across the eastern U.S. by

3.7 ppb based on likely emission levels. It is assumed that the regional air quality plan would be 

adjusted accordingly to compensate for this expected increase. Thus, the Houston-Galveston regional 

emissions of both NOx and VOCs were proportionately reduced to maintain attainment of the current 8-
 TFA Assessment

17

hour ground level ozone standard of 75 ppb.8 While less specific data is available for the South Coast, 

IPCC projections report significant increase in the frequency and magnitude of ground level 

temperature, which leads to higher ozone concentrations. Thus, it is assumed that the same level of 

increase in background ozone concentration would be seen for the South Coast region as projected for 

the eastern United States. As a result, regional emissions for the South Coast after 2023 were also 

proportionately reduced to account for the expected 3.7 ppb increase.

Data from scenario 2 (described above in Table 3) were used to project the amount of HFO-1234yf 

(metric tons, MT, per day) emitted in the Houston-Galveston and South Coast regions. The annual 

output shown in Annex A was adjusted according to the population of the Houston-Galveston and South 

Coast regions. Emissions from the MVAC and stationary AC end uses were multiplied by 59.5% and then 

divided by 153 days/year (number of days in the summer ozone season) to determine the higher 

summer seasonal daily emission rate for HFO-1234yf.9 Refrigeration emissions were assumed to be 

uniformly distributed throughout the year. These data were then used to make two sets of projections 

concerning the production of ground level ozone. One set of projections assumes the reactivity of HFO1234yf to be the same as the average VOC. The other set of projections assumes HFO-1234yf is more 

reactive and has the maximum potential to form up to 3 molecules of ozone per molecule of HFO1234yf.10 This assumption implies that one tonne of HFO-1234yf emissions has an equivalent impact on 

air quality as 3 tonnes of emissions of average VOC. 

The emission projections of NOx, VOC, and HFO-1234yf in the Houston-Galveston and South Coast 

region are summarized in Table 10 and Table 11.

Table 10: Projected Emissions of NOx, VOC, and HFO-1234yf in the Houston-Galveston region of Texas (MT/day)

Year NOx VOC HFO-1234yf 3x HFO-1234yf

2019 764 378 0.47 1.41

2029 753 373 2.61 7.84

2040 741 367 3.59 10.78

2050 730 362 4.13 12.38

Source: Post-1999 Rate-of-Progress and Attainment Demonstration SIP for the Houston/Galveston Ozone Nonattainment Area 

(Texas Natural Resource Conservation Commission, 2000) 

* Includes the counties of Brazoria, Chambers, Fort Bend, Galveston, Harris, Liberty, Montgomery and Waller

 

8

For both Houston and Los Angeles the ozone attainment demonstrations emission reductions were based on the 

prior 80 ppb 8-hour ozone standard. Additional emission reductions will be needed to reach the new 75 ppb 8-

hour standard. It is assumed that a linear reduction for both VOC and NOx would be needed to reach this new 

standard and impacts of HFO-1234yf were evaluated based on these lower emission rates. 

9 Hoffpauir, Elvis. 2009. Email to Karen Thundiyil, 10 March; U.S. EPA Vintaging Model, Version VM IO File v4.2 10-

07-08

10 In discussions with Dr. Ravishankara, the director of the Chemical Sciences Division of the National Oceanic and 

Atmospheric Administration (NOAA) Earth System Research Laboratory in Boulder, Colorado, it was indicated that 

HFO-1234yf has the potential to form up to 3 molecules of ozone per molecule of HFO-1234yf reacted hydroxyl 

radical. 
 TFA Assessment

18

Table 11: Projected Emissions of NOx, VOC, and HFO-1234yf in the South Coast* region of California (MT/day)

Year NOx VOC HFO-1234yf 3x HFO-1234yf

2017 335 392 0.73 2.19

2023 280 355 5.14 15.41

2040 272 345 14.40 43.19

2050 268 339 16.54 49.63

Source: South Coast AQMD 2007 Future Year Emission Inventory (South Coast, 2007)

*Includes the counties of Kern, Imperial, Los Angeles, Orange, Riverside, San Bernardino, San Luis Obispo, San Diego, Santa 

Barbra and Ventura 

For Houston-Galveston the ratio of the 3x HFO-1234yf to the 2019 VOC emission rate shows that ground 

level ozone potentially could increase by less than 1% (0.37%= 1.41/378) assuming a VOC-limited 

environment, or an environment where ozone formation is limited by the availability of VOC (not the 

availability of NOx). However, if the reactivity of HFO-1234yf is assumed to be the same as the average 

VOC (as opposed to forming 3 molecules of ozone per molecule of HFO-1234yf), it is predicted that 

ground level ozone would increase by an even lesser percentage (0.12%= 0.47/378). By 2029, the 

potential increases in ground level ozone could be as high as 1% - 2 % depending on the reactivity of 

HFO-1234yf. 

For the South Coast the ratio of the 3x HFO-1234yf to the 2023 VOC emission rate shows that ground 

level ozone potentially could increase by about 4.3% (= 15.41/355) assuming a VOC limited 

environment. However, if the reactivity of HFO-1234yf is assumed to be the same as the average VOC

(as opposed to forming 3 molecules of ozone per molecule of HFO-1234yf), then ground level ozone 

would increase by about 1.4% (=5.14/355).

These percentage increases in ozone suggest how much ground level ozone may potentially increase as 

a result of the use of HFO-1234yf, relative to the projected emissions of NOx and VOC. Both of these 

regions have detailed plans to achieve attainment of the 8-hour ozone standard. In Houston, reaching 

attainment by 2019 would imply having a maximum 8-hour ozone concentration of no more than 75 

ppb. If HFO-1234yf was 3x as reactive as the average VOC, HFO-1234yf emissions could potentially 

contribute 0.3 ppb to the regional ozone concentration by 2019. Assuming that the Houston regional 

plan is set to achieve exactly the 75 ppb 8-hour ozone concentration standard in 2019, an additional 

contribution of 0.3 ppb to the regional ozone concentration could cause the total concentration to reach 

75.3 ppb, which would be considered non-attainment. Similarly, for South Coast region, in 2023 HFO1234yf emissions could contribute 3.2 ppb to the regional ozone concentration, if HFO-1234yf was 3x as 

reactive as the average VOC. An additional contribution of 3.2 ppb could cause the total concentration 

to reach 78.2 ppb, which would be considered non-attainment. 

Emissions of NOx and VOC will likely continue to decrease for both the Houston-Galveston and the South 

Coast area,11 and HFO-1234yf emissions are projected to increase (see Annex A), but it is uncertain to 

what extent these combined changes will impact local air quality in years after 2030. There is the 

potential for continued increases in ground level ozone from increases in both background 

concentrations and from the contribution from HFO-1234yf emissions and other VOC emissions sources; 

however, uncertainties related to the impacts from global warming, changes in control technology, and 

 

11 South Coast AQMD 2007 Future Year Emission Inventory (South Coast, 2007); Post-1999 Rate-of-Progress and 

Attainment Demonstration SIP for the Houston/Galveston Ozone Nonattainment Area (Texas Natural Resource 

Conservation Commission, 2000).
 TFA Assessment

19

changes in emission sources do not allow a detailed analysis to be conducted at this time. Additionally, 

it is expected that air quality planners in regions such as Houston and the South Coast would seek to 

offset significant emission increases of HFO-1234yf with emissions reductions from other VOC source 

categories. Even so, depending upon the spatial and temporal distribution of HFO-1234yf emissions, 

there is potential that these emissions could contribute to the production of ground level ozone and 

potentially contribute to non-attainment or exacerbate existing non-attainment in a given region.

For other areas of the United States that were not examined in this analysis, a similar conclusion can be 

drawn: HFO-1234yf emissions have the potential to increase ground level ozone; however, the percent 

increase of 1% – 4% is not expected to impact other regions as severely. Most other areas are not VOClimited meaning that their ozone concentrations are not affected by additional VOC emissions. 

Furthermore, it is expected that less severe regions will achieve the ozone standard by 2013,12 thus 

retaining some additional margin of safety. Because the two regions, Los Angeles and Houston, are 

expected to reach attainment coincident with the rapid market penetration of HFO-1234yf in the late 

2010’s, these two regions are representative of those most susceptible to being pushed backed into 

non-attainment as a result of ozone formation from HFO-1234yf emissions.

5.3. Limitations of this Analysis

The analysis described above is based on numerous assumptions and projections that cannot be known 

with certainty at this time. The following discussion recognizes these uncertainties and indicates various 

factors that have potential to impact and change the results of this analysis. 

5.3.1. Market Modeling

 The market penetration assumptions used for this analysis assume HFO-1234yf will be the sole 

replacement for HFC-134a. However, the introduction of additional substitutes could 

potentially lower the penetration of HFO-1234yf into the market, thus decreasing the emissions 

and impacts of HFO-1234yf and TFA.

 Even though EPA’s Vintaging Model, used to calculate emissions for both scenarios, provides 

output up to 2050, the assumptions used in the model are based only on current data and 

expert opinions regarding the near future. Since it is not possible to predict with certainty 

changes that will occur in the distant future (post 2020), the assumptions in the model are not 

adjusted for additional unpredictable changes that will likely take place.

 EPA’s Vintaging Model does not account for reductions in emissions that may occur as a result 

of using HFO-1234yf as a replacement for HFC-134a. Factors such as refrigerant price and 

advancements in leak-tightness of MVAC systems are not adjusted for in the modeling. 

Consequently, HFO-1234yf emission projections are considered to be conservative.

5.3.2. Aquatic and Soil Impacts

 

12 Environmental Protection Agency. Accessed May 2009. Classifications of 8-Hour Ozone Nonattainment Areas. Last Updated 

March 12, 2009. Available at <http://www.epa.gov/air/oaqps/greenbk/gnc.html>
 TFA Assessment

20

 The modeling of potential future impacts to plant and animal species adapted to vernal pool 

ecology may be overestimated using the models described. This is due to human population 

differences in the area of southern CA, which is modeled in section 5.1, to the populations 

currently living in the areas known to have recurrent vernal pools (e.g., Central Valley of CA). 

Nevertheless, it is important to assume maximum impact based on emissions modeling due to 

the persistent nature of TFA in the environment. 

 A significant source of uncertainty in the analysis of aquatic toxicity is the receptor species used 

in the analysis. For example, in the cited studies, researchers used widely accepted and 

standardized species of freshwater flora and fauna. These plant and animal species, however, 

are not typical of specialized vernal pool species in California such as meadow foam, Downingia, 

Navarettia, fairy shrimp, tadpole shrimp, or tiger salamanders. Of course, one reason for this is 

that many of these species are endangered and/or protected, and it is not possible to conduct 

toxicity studies on them. Nevertheless, lack of knowledge regarding the susceptibility and/or 

resistance to TFA or similar compounds by these species affects the ability to more accurately 

quantify aquatic impacts from TFA deposition in certain geographical areas.

 The ecology considered in this analysis is a highly specialized one that is vital to many species, 

including migratory birds. In addition, regional areas that contain the geology necessary for 

vernal pool formation are subject to modification via many means, including residential and 

commercial development, mining, agriculture, and in California, earthquakes. These activities 

also produce environmental contamination that affects species adapted to vernal pool ecology. 

It is not possible to predict the impact of these external effects on aquatic toxicity of vernal 

pools, nor how TFA concentrations, in concert with these other effects, might change the 

estimated results presented here.

5.3.3. Air Quality 

 Improvements in the understanding of the reactivity of HFO-1234yf and resulting production of 

TFA and ozone formation are likely to change the estimates made in this analysis. 

 Further global warming impacts will result in region-specific changes that may for example 

increase local cloud cover leading to decreases in local photolysis rates resulting in reduced 

ozone production.

 The changes in standards for other pollutants such as air toxics or criteria pollutants could effect 

the precursor ozone emissions. For example, EPA recently announced a proposed rule for a new 

1-hour NO2 standard in the range between 80 to 100 ppb. In order to meet this standard, 

significant NOx emission reductions may be required, thus impacting the potential production of 

ground level ozone.

 The ozone air quality standard may be lowered in the future (historically the standard has been 

lowered a number of times) and would require additional reductions of ozone precursor 

emissions, which would increase the importance of HFO-1234yf to the production rate for 

ozone.
 TFA Assessment

21

6. Conclusion

From the analysis summarized in the previous sections of this white paper, the following preliminary 

conclusions concerning the potential impacts of HFO-1234yf and the associated production of TFA can 

be made:

 Projected levels of TFA in rainwater should not result in a significant risk of ecotoxicity. After 

taking into account the nature of HFO-1234yf degradation and the resulting TFA concentration in 

rainwater; regional precipitation patterns; the geology of closed aquatic systems; and no 

observed effect concentrations (NOEC) for TFA, TFA production resulting from HFO-1234yf 

emissions is not expected to pose significant harm to aquatic communities in the near future. 

Future research is necessary to determine if significant TFA loading is occurring in vernal pools 

near major population centers as there are insufficient data to determine whether TFA would 

impact these environments significantly.

 Dry Deposition is somewhat of a concern however more research is needed to fully understand 

the impacts of dry deposition on soil, plants, and aquatic communities. Only two studies were 

identified which investigated the effects of dry deposition in plants. While one study showed 

measured effects on photosynthesis, the other did not. It is unclear what impact current and 

future loading of TFA will have in vernal pool ecosystems. Current tests on freshwater plants and 

animal species that might be found in vernal pools show that only one species of algae might be 

affected at predicted concentrations of deposited TFA. However, it is not possible to know

without further research, whether increased TFA loading might affect other obligate vernal pool 

species. 

 Non-attainment resulting from HFO-1234yf emissions is not likely to be a major concern for 

local air quality in most locations. HFO-1234yf could potentially increase ground level ozone by 

1% to 4% on a given day in the most extreme case. However, in most cases this upper bound 

level of increase is not likely, as most ozone nonattainment areas are (1) not VOC limited and (2) 

the HFO-1234yf-mediated ozone production is more likely to be closer to a single molecule 

rather than conservative 3 molecules used in this assessment. Both of these conditions would 

reduce the potential increase in ground level ozone to at most a 1% to 2% increase. However, 

given the variety of uncertainties, it is difficult to predict how future TFA emissions will impact 

non-attainment of the ozone NAAQS on these days. These uncertainties include the composition 

of the future atmosphere, the extent of increases or decreases in ground level ozone from other 

sources, the reactivity of HFO-1234yf under near- and later-term atmospheric conditions, 

impacts on reactivity and circulation associated with global warming, and, most importantly, the 

future measures that may be taken to reduce ozone precursors. 
 TFA Assessment

22

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Annex A: Annual HFO-1234yf Emissions Estimated under each Scenario for the

Years 2010 through 2050 (MT)*

Year Scenario 1 Scenario 2

MVACs MVACs Refrigeration Stationary AC TOTAL

2010 - - 31 6 37

2011 - - 96 18 114

2012 - - 194 37 231

2013 - - 329 62 392

2014 - - 502 94 597

2015 - - 715 134 849

2016 407 407 1,034 192 1,633

2017 1,229 1,229 1,465 269 2,963

2018 2,472 2,472 2,014 365 4,851

2019 4,143 4,143 2,685 481 7,309

2020 6,244 6,244 3,484 617 10,345

2021 8,332 8,332 4,304 761 13,397

2022 10,413 10,413 5,169 910 16,493

2023 12,513 12,513 6,031 1,061 19,605

2024 14,644 14,644 6,926 1,212 22,782

2025 16,812 16,812 7,817 1,363 25,992

2026 19,003 19,003 8,702 1,512 29,217

2027 21,203 21,203 9,580 1,675 32,457

2028 23,962 23,962 10,505 1,845 36,313

2029 26,335 26,335 11,373 2,014 39,722

2030 28,327 28,327 12,261 2,212 42,800

2031 29,927 29,927 13,084 2,405 45,415

2032 31,121 31,121 13,836 2,571 47,529

2033 31,301 31,301 14,420 2,716 48,437

2034 31,526 31,526 15,013 2,860 49,398

2035 31,811 31,811 15,509 3,009 50,328

2036 32,114 32,114 16,040 3,212 51,366

2037 32,418 32,418 16,576 3,408 52,402

2038 32,687 32,687 17,118 3,594 53,399

2039 32,936 32,936 17,664 3,770 54,371

2040 33,196 33,196 18,216 3,936 55,349

2041 33,476 33,476 18,731 4,014 56,221

2042 33,801 33,801 19,245 4,087 57,133
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Year Scenario 1 Scenario 2

MVACs MVACs Refrigeration Stationary AC TOTAL

2043 34,110 34,110 19,758 4,160 58,028

2044 34,425 34,425 20,269 4,228 58,922

2045 34,748 34,748 20,779 4,290 59,818

2046 35,079 35,079 21,274 4,329 60,682

2047 35,417 35,417 21,781 4,367 61,565

2048 35,763 35,763 22,301 4,400 62,464

2049 36,116 36,116 22,834 4,433 63,383

2050 36,478 36,478 23,379 4,467 64,324

* ICF projected emissions of HFO-1234yf using special scenarios designed specifically for this analysis and run on 

the U.S. EPA Vintaging Model, Version VM IO file v4.1 5-19-09. 
 TFA Assessment

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Annex B: Estimated Production of TFA under each Scenario, by year (MT)

Year Scenario 1 Scenario 2

MVACs MVACs Refrigeration Stationary AC TOTAL

2010 - - 28 5 34

2011 - - 86 16 103

2012 - - 175 33 208

2013 - - 297 56 353

2014 - - 452 85 537

2015 - - 643 120 764

2016 366 366 931 173 1,469

2017 1,106 1,106 1,319 242 2,667

2018 2,225 2,225 1,812 329 4,366

2019 3,729 3,729 2,416 433 6,578

2020 5,620 5,620 3,136 555 9,311

2021 7,499 7,499 3,873 685 12,057

2022 9,372 9,372 4,652 819 14,843

2023 11,262 11,262 5,428 955 17,645

2024 13,180 13,180 6,234 1,090 20,504

2025 15,131 15,131 7,035 1,227 23,393

2026 17,103 17,103 7,831 1,361 26,295

2027 19,083 19,083 8,622 1,507 29,212

2028 21,566 21,566 9,455 1,661 32,681

2029 23,702 23,702 10,235 1,813 35,750

2030 25,494 25,494 11,035 1,991 38,520

2031 26,934 26,934 11,775 2,164 40,874

2032 28,009 28,009 12,453 2,314 42,776

2033 28,171 28,171 12,978 2,444 43,593

2034 28,373 28,373 13,511 2,574 44,458

2035 28,630 28,630 13,958 2,708 45,295

2036 28,902 28,902 14,436 2,891 46,229

2037 29,176 29,176 14,918 3,068 47,162

2038 29,418 29,418 15,406 3,235 48,059

2039 29,643 29,643 15,898 3,393 48,934

2040 29,877 29,877 16,395 3,543 49,814

2041 30,129 30,129 16,858 3,613 50,599

2042 30,421 30,421 17,320 3,679 51,420

2043 30,699 30,699 17,782 3,744 52,225
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Year Scenario 1 Scenario 2

MVACs MVACs Refrigeration Stationary AC TOTAL

2044 30,983 30,983 18,243 3,805 53,030

2045 31,273 31,273 18,701 3,861 53,836

2046 31,571 31,571 19,147 3,896 54,614

2047 31,875 31,875 19,603 3,930 55,409

2048 32,186 32,186 20,071 3,960 56,217

2049 32,505 32,505 20,550 3,990 57,045

2050 32,830 32,830 21,042 4,020 57,892