Document ID: EPA-HQ-OAR-2008-0664-0215
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2011-02-28T05:00Z

MEMORANDUM

To:	Margaret Sheppard , U.S. EPA 

CC:	Yaidi Cancel, U.S EPA

From:	Emily Herzog, Ed Carr, Kara Altshuler, Veronica Kennedy, Mark
Wagner, ICF International 

Date:	May 25, 2010

Re:	Revised Assessment of the Potential Impacts of HFO-1234yf and the
Associated Production of TFA on Aquatic Communities, Soil and Plants,
and Local Air Quality (Deliverable under EPA Contract Number EP-W-06-008
Task Order 038, Task 06)

Please find attached a revised version of a paper that examines the
emissions of HFO-1234yf and the associated production of TFA under
several scenarios.  The assessment has been revised to reflect a revised
approach to analyzing impacts of HFO-1234yf emissions.  This approach
used EPA’s CMAQ model version 4.7 with the chemical mechanism
incorporating chemistry and reaction rates for HFO-1234yf transformation
to TFA.  The results from this analysis confirm our previous conclusions
that projected emissions of HFO-1234yf should not result in a
significant risk to aquatic communities, soil and plants, or local air
quality.

Please contact Mark Wagner at 202-862-1155 with any questions or
comments.



Assessment of the Potential Impacts of 

HFO-1234yf and the Associated Production of TFA on Aquatic Communities,
Soil and Plants, and Local Air Quality

Prepared for:

Stratospheric Protection Division

Office of Atmospheric Programs

U.S. Environmental Protection Agency

1310 L Street, NW

Washington, DC  20005

Prepared by:

ICF International 

1725 Eye Street, NW, Suite 1000

Washington, DC 20006

May 25, 2010

Table of Contents

  TOC \o "1-3" \h \z \u    HYPERLINK \l "_Toc262138132"  Foreword	 
PAGEREF _Toc262138132 \h  i  

  HYPERLINK \l "_Toc262138133"  Executive Summary	  PAGEREF
_Toc262138133 \h  1  

  HYPERLINK \l "_Toc262138134"  1.	Introduction	  PAGEREF _Toc262138134
\h  1  

  HYPERLINK \l "_Toc262138135"  2.	Production and Environmental Fate of
Trifluoroacetic acid (TFA)	  PAGEREF _Toc262138135 \h  3  

  HYPERLINK \l "_Toc262138136"  3.	Toxicity of Trifluoroacetic Acid
(TFA)	  PAGEREF _Toc262138136 \h  4  

  HYPERLINK \l "_Toc262138137"  3.1.	Aquatic and Environmental Toxicity	
 PAGEREF _Toc262138137 \h  4  

  HYPERLINK \l "_Toc262138140"  3.2.	Human and Animal Toxicity	  PAGEREF
_Toc262138140 \h  8  

  HYPERLINK \l "_Toc262138141"  4.	Assessment of Potential HFO-1234yf
Emissions	  PAGEREF _Toc262138141 \h  10  

  HYPERLINK \l "_Toc262138142"  4.1.	Scenarios of HFO-1234yf Market
Penetration	  PAGEREF _Toc262138142 \h  10  

  HYPERLINK \l "_Toc262138143"  4.2.	HFO-1234yf Emission Assumptions	 
PAGEREF _Toc262138143 \h  11  

  HYPERLINK \l "_Toc262138144"  4.3.	Estimated Emissions of HFO-1234yf	 
PAGEREF _Toc262138144 \h  11  

  HYPERLINK \l "_Toc262138149"  5.	Assessment of Potential Impacts of
HFO-1234yf and TFA	  PAGEREF _Toc262138149 \h  13  

  HYPERLINK \l "_Toc262138150"  5.1.	TFA Rainwater Concentrations	 
PAGEREF _Toc262138150 \h  13  

  HYPERLINK \l "_Toc262138151"  5.2.	TFA Dry Deposition	  PAGEREF
_Toc262138151 \h  14  

  HYPERLINK \l "_Toc262138152"  5.3.	Ground Level Ozone Concentrations	 
PAGEREF _Toc262138152 \h  15  

  HYPERLINK \l "_Toc262138153"  6.	Discussion of Results	  PAGEREF
_Toc262138153 \h  16  

  HYPERLINK \l "_Toc262138154"  6.1.	Summary of Findings	  PAGEREF
_Toc262138154 \h  17  

  HYPERLINK \l "_Toc262138155"  6.2.	Limitations of this Analysis	 
PAGEREF _Toc262138155 \h  17  

  HYPERLINK \l "_Toc262138156"  7.	References	  PAGEREF _Toc262138156 \h
 20  

  

Foreword

In a previous analysis conducted in the Spring/Summer of 2009, ICF
International assessed the potential impacts of HFO-1234yf emissions and
the associated production of TFA on aquatic communities and local air
quality.  Using the research and resources available at the time, ICF
made numerous conservative assumptions regarding the potential emissions
and atmospheric reactivity of HFO-1234yf.  

Specifically, in the earlier assessment, ICF scaled emissions of SO2
proportionately to the projected emissions of HFO-1234yf based on the
understanding that the lifetime cycle for SO2 to sulfate conversion and
removal in cloud droplets is similar to that of HFO-1234yf to TFA
removal in cloud droplets.  ICF then applied EPA’s three-dimensional
community multiscale air quality model (CMAQ) using emissions of SO2
only from the Los Angeles and Houston air basins to determine the dry
sulfate deposition and sulfate rainwater concentrations for a typical
one-year (2001) period using hourly meteorological data.   The sulfate
concentrations were then scaled on an 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.

The results from the earlier analysis estimated the highest monthly
average TFA concentration in rainwater to be 1.8 mg/L in 2050 located
downwind of Los Angeles, and only 0.008 mg/L downwind of Houston for the
same year.  The maximum concentrations in both annual and monthly
rainwater for Houston were well below the 0.12 mg/L no observed effect
concentration (NOEC) reported for the most sensitive freshwater green
algae species tested at the time.   However, Los Angeles showed 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.   In addition, beginning sometime
between 2025 and 2030, it was estimated that the rainwater
concentrations could exceed the NOEC of 1 mg/L for vernal pool plant
species in vernal pools near Los Angeles during the month of July. 
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 were estimated to be significantly below the NOECs for all
vernal pool species.  

In regards to dry deposition of TFA, ICF found that the monthly peak dry
deposition occurred in March for Los Angeles and in July for Houston. 
The modeling results indicated 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.  However,
current toxicity data on ecological receptors indicated that TFA has low
toxicity for most aquatic microbial, plant, and animal species; does not
bioconcentrate; and does not appear to have effects on germination on
those species tested.  .

To estimate potential impacts on local air quality, ICF assumed the
ozone creation from the release of HFO-1234yf to be similar to that of
the volatile organic compound (VOC) ethylene, as described by
Papadimitriou et al. (2008).  The Houston-Galveston region and the South
Coast Air Basin in California were again 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 was 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-hour ground level ozone standard of 75 ppb.  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 was
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 in ozone due to global warming.

Results from this earlier analysis showed that for Houston-Galveston
ground level ozone potentially could increase by less than 1%, assuming
a VOC-limited environment, or an environment where ozone formation is
limited by the availability of VOC (not the availability of NOx).  For
the South Coast (i.e., around Los Angeles), ground level ozone was
expected to increase by about 1.4%.  These percentage increases in ozone
suggest how much ground level ozone could potentially increase as a
result of the use of HFO-1234yf, relative to the projected emissions of
NOx and VOC over time.  For other areas of the United States that were
not examined in the analysis, a similar conclusion was drawn: HFO-1234yf
emissions have the potential to increase ground level ozone; however,
the percent increase is expected to impact other regions to a much
lesser extent. 

Given the limitations and conservative nature of this earlier analysis,
ICF concluded that (a) projected levels of TFA in rainwater should not
result in a significant risk of ecotoxicity; (b) 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; and (c) non-attainment resulting from HFO-1234yf emissions
is not likely to be a major concern for local air quality in most
locations.

Since the completion of the analysis, new information and findings have
been brought to the attention of ICF.  As a result, the analysis has
been revised and is described in the remainder of this paper.

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 reactivity that could potentially lead to increased
levels of ground-level 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, the maximum amount of dry deposited
TFA, and the potential increase in ground level ozone.  From this
analysis, it was concluded that the projected maximum concentration of
TFA in rainwater and the amount of TFA dry deposited 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.

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 low-GWP 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.  

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., 2008).

Although the use of HFO-1234yf could potentially mitigate greenhouse gas
emissions, it could also potentially contribute to increased levels of
ground level ozone.  While the maximum incremental reactivity of
HFO-1234yf is expected to be similar to that of ethane (Carter 2009), it
is possible that in some locations the reactivity could be considerable
higher depending on regional conditions.  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 (Boutonnet 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 HFO-1234yf; 

Section 5 discusses the results of this analysis and presents an
assessment of the potential impacts on aquatic ecosystems and local air
quality; and

Section 6 discusses the results and identifies the limitations of the
analysis. 

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 11
days on average before they are encapsulated into water droplets and
hydrolyzed to TFA (Papadimitriou et al., 2008).  

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 (n-octanol/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 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 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.

ow concentrations (≤30 mg F/L) over the span of 100 weeks in small (10
L) fermentation batches of a mixture of unidentified bacteria.  The
issue of environmental degradation of TFA is a subject of continuing
research and the data currently do not allow one to predict whether this
environmental sink will moderate TFA loading in the future.

Toxicity of Trifluoroacetic Acid (TFA)

Aquatic and Environmental Toxicity

TFA is mildly toxic to plant life (i.e., phytotoxic).  In certain
environmental conditions, TFA might 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, certain aquatic plant species, small invertebrates, and
segmented worms (such as earthworms), do not accumulate large quantities
of TFA, and are not significantly impacted by the compound (Berends et
al. 1999; 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   REF _Ref215975377 \h  Table 1 
below).  

Lowest observed effect concentrations (LOEC) and no observed effect
concentrations (NOEC), as summarized by Boutonnet et al. (1999), are
shown in   REF _Ref215975377 \h  Table 1 .  Note that values are listed
both for the sodium salt of TFA (NaTFA) and estimated equivalent TFA, in
parentheses.  Boutonnet et al. (1999) measured NaTFA, because the free
acid itself is not likely to be present at high concentrations in
environmental media.

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

Aquatic Organisms	EC50a	LOECb	NOECc 

Selenastrum capricornutum 

(freshwater green alga) 

(new name: Pseudokirchneriella subcapitata)	4.8 (4.0)d 

>1.2 (1.0)	0.36 (0.30)e	<0.36 (0.30)

0.12 (0.1)

Anabaena flos-aquae 

(blue-green alga)	2400 (2011) 	1200 (1000)	600 (500)

Navicula pelliculosa 

(freshwater diatom)	1200 (1000) 	1200 (1000)	600 (500)

Skeletonema costatum 

(marine diatom)	---	---	2400 (2011)

Chlorella vulgaris 

(freshwater green alga)	---	---	1200 (1000)

Chlamydomonas reinhardtii

 (freshwater green alga)	---	---	>120 (>100)

Microcystis aeruginosa 

(blue-green alga)	---	---	>117 (98)

Phaeodactylum tricornutum 

(marine alga)	---	---	>117 (98)

Dunaliella tertiolecta

 (marine alga)	---	---	>124 (104)

Euglena gracilis 

(freshwater alga)	---	---	>112 (94)

Daphnia magna 

(crustacea)	---	---	1200 (1000)

Brachydanio rerio 

(Zebra fish)	---	---	1200 (1000)

Lemna gibba 

(duckweed) --- vegetative growth	1100 (920)	600 (500)	300 (250)

a EC50 = test concentration resulting in an effect in 50% of the
organisms tested; the table lists EC50 for biomass integral (adverse
effects on growth)

b LOEC = lowest observed effect concentration 

c NOEC = no observed effect concentration (defined as the lowest
concentration for which the effects were not statistically different
from the controls)

d Values provided in parentheses represent the data normalized to TFA,
mg/L

e At this concentration, the inhibition of the biomass integral was 11%.

Source: Boutonnet et al. 1999

s of NaTFA (≥300 mg/L; ca. 250 mg TFA/L) did not result in adverse
effects in the fish, crustacean, and diatom species tested, and most of
the algal species tested.  In duckweed, mild negative growth effects
were seen on frond and weight increase at 600 mg/L; no effects were
noted at 300 mg/L. Toxicity tests conducted with select species of algae
shown above are taken from a study by Berends et al. (1999) who found
that, for ten of the eleven species tested, the effect concentration for
50% of the test organisms (EC50) was >100 mg/L NaTFA (ca 84 mg TFA/L). 
The lowest threshold for effects was observed for the unicellular alga,
Pseudokirchneriella subcapitata (formerly S. capricornutum), which is
commonly used as an indicator species in ecotoxicity screening tests. 
Toxicity results varied among the different labs testing P. subcapitata
as reported by these authors (Berends et al. 1999); the authors state
that responses at the low range of test concentrations were generally
consistent, however, and they consider 0.12 mg NaTFA/L (0.10 mg TFA/L)
to be the threshold for toxicity (e.g., no effects on growth were noted
at this concentration).  However, at higher concentrations TFA did not
have an algicidal effect, but rather an algistatic (e.g., slowing
growth) effect on this species, as growth resumed three days after the
TFA was removed (Berends et al. 1999).

Environmental receptors in seasonal wetlands vary with geography, and
are established in unique ecosystem niches.  Plant species tend to be
annuals, as perennials are not adapted to the seasonality of the
rainfall.  Animal species, such as the 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. They are adapted to inconsistent levels of rainfall year
to year, and varying pH and salinity gradients, and typically mature
from egg to reproductive-age adult in a matter of weeks.  As TFA
exposure studies with these species are unavailable, there is no
definite information regarding what, if any, effects increasing TFA
concentrations would have on the life cycle of these niche organisms or
others.  Existing data on other similar organisms, however, indicate no
cause for concern. 

Additional data taken from more recent articles relative to the toxicity
of TFA in fish, aquatic plants, and freshwater benthic microbial
communities are shown in   REF _Ref215975430 \h  Table 2 . They indicate
that TFA exhibits low toxicity in these receptors. 

Table   SEQ Table \* ARABIC  2 : Summary of Additional Toxicity Studies
of Trifluoroacetate (mg/L)

Aquatic Organisms	EC50/LC50a	LOECb	NOECb

Brachydanio rerio (Zebra fish) 

(Wiegand et al., 2000)	---	1,000  (1,200)c

(low elevation of GST activity)	4,000 (4,770)

(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 

(265-12,000)	M. sib.: 300  (360)

M. spic.: 100 (120)

L. gibba: 100 (120) 	M. sib.: 100 (120)

M. spic.: 30 (36)

L. gibba: 30 (36)

Pimephales promelas (Fathead minnow) (Geiger et al., 1988, as cited in
ECOTOX)	7.79 - 1.28 

(9.3-1.5)	---	---

Freshwater benthic microbial communities in stream sediments (Bott and
Standley, 1998)	---	---	0.00002 to 0.2 (0.000024 to 0.24)(no effect on
acetate metabolism)

a EC50 = test concentration resulting in an effect in 50% of the
organisms tested; the table lists EC50 for biomass integral (adverse
effects on growth); LC50 = lethal concentration for 50% of the tested
organisms

b LOEC = lowest observed effect concentration; NOEC = no observed effect
concentration

c Glutathione S-transferase

The combined impact of TFA and other haloacetic acids in the environment
is unlikely 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 (aquatic plants) 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
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 bioconcentration factor (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 BCFs derived
in studies with green algae (BCF of approximately 10; van Dijk 1996, as
cited in Boutonnet et al. 1999) and duckweed (BCF of 1.0 to 1.6; Smyth
et al. 1993, as cited in Boutonnet et al., 1999). 

As seasonal wetlands evaporate, TFA can remain in place and could
concentrate over time, resulting in long-term accumulation. However,
vernal pools have varying levels of seepage due to lateral movement of
sub-surface ground water flow, or because of weak or broken hardpans at
the bottom of the pools (Sefchick et al. 1994, as quoted in Boutonnet et
al. 1999; Hanes, 1998).  TFA accumulation is not expected in pools
exhibiting seepage. Of course, as these wetlands go dry, any TFA salt
present would be adsorbed to soil particles on the ground surface, and
would be subject to other transport mechanisms, such as removal by wind,
etc.   Potential TFA accumulation may be linked to increased
concentrations of TFA in plants in these wetlands, but again, plants in
seasonal wetlands are heavily represented by annual grasses and similar
species and TFA has been shown not to affect seed production for future
propagation in these ecosystems.  

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 10- to 60-fold lower than
the lowest reported NOEC of 0.12 mg/L for the most sensitive species of
freshwater green algae (P. subcapitata). 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

Current risk assessments indicate that vernal pool species would not be
negatively impacted with current and predicted published estimates of
TFA loading in the environment.

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. 

Assessment of Potential HFO-1234yf Emissions 

This analysis is intended as a screening exercise to develop a
reasonable worst-case estimate of HFO-1234yf emissions under various use
scenarios. The remainder of this section describes the assumptions used
for this analysis to determine potential emissions of HFO-1234yf.  A
discussion on the limitations of the emission projections of HFO-1234yf
can be found in section 6.1 of this paper.

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,
with a replacement ratio of 1:1 HFC-134a to HFO-1234yf.    The market
penetration scenarios are described below and summarized in   REF
_Ref215975477 \h  Table 3 .

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   REF _Ref215975477 \h  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. 

Table   SEQ Table \* ARABIC  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%

*The dates of introduction of HFO-1234yf are consistent with the earlier
analysis, conducted in 2009 and explained in the foreword of this
document.  

The specific dates of introduction are used as a demonstration of how
HFO-1234yf might be phased in; actual dates may differ by several years.
 Examining the period from initial introduction of the refrigerant to
market saturation allows the analysis to consider potential impacts of
HFO-1234yf in the near-term (i.e., 10 - 15 years), during which time
there are already specific State goals for ground-level ozone impacts. 
In addition, the analysis considers the potential longer term impacts of
HFO-1234yf after the refrigerant has saturated the market, assuming
continued growth in motor vehicle use.

HFO-1234yf Emission Assumptions

ICF assumed that emissions of HFO-1234yf will be equivalent to emissions
of HFC-134a.  Emission assumptions from the MVAC sector for this
analysis are summarized below in   REF _Ref258934555 \h  \* MERGEFORMAT 
table 4 .

Table   SEQ Table \* ARABIC  4 : Refrigerant Loss Assumptions from the
MVAC Sector

Assumption	Emissions Ratea

Leak Rate	8%

Servicing Leaks (annualized)	10%

End-of-life Loss Rate	42.5%

a HFC-134a MVAC assumptions from the U.S. EPA Vintaging Model, Version
VM IO File v4.4_12-16-09.   

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. 
Furthermore, refrigerant emissions from servicing motor vehicle air
conditioning systems were estimated at 47% of annual refrigerant
emissions from motor vehicles.  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.

Estimated Emissions of HFO-1234yf

Using EPA’s Vintaging Model, ICF estimated emissions of HFO-1234yf for
both scenarios.  These estimates are summarized in   REF _Ref215975548
\h  Table 5  while estimated monthly emission estimates of HFO-1234yf
for the year 2050 are provided in   REF _Ref258940654 \h  Table 6 . 
Estimated annual HFO-1234yf emissions under each scenario are also
graphically depicted in Figure 1 and Figure 2.  A complete table with
estimated annual emissions can be found in Annex A.  

Table   SEQ Table \* ARABIC  5 : Summary of Estimated Emissions of
HFO-1234yf (MT)*

Scenarios	2020	2030	2040	2050

Scenario 1	6,244	28,327	33,093	35,851

Scenario 2	10,501	43,296	55,070	60,616

* 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 v4.4_12-16-09.   

Table   SEQ Table \* ARABIC  6 : Summary of Estimated Monthly Emissions
of HFO-1234yf in 2050 (MT)

Scenarios	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec

Scenario 1	2,074	2,074	2,074	4,266	4,266	4,266	4,266	4,266	2,074	2,074
2,074	2,074

Scenario 2	4,025	4,025	4,025	6,489	6,489	6,489	6,489	6,489	4,025	4,025
4,025	4,025

Figure   SEQ Figure \* ARABIC  1 : Estimated Emissions of HFO-1234yf by
End-Use Sector under Scenario 1 (MT)

Figure   SEQ Figure \* ARABIC  2 : Estimated Emissions of HFO-1234yf by
End-Use Sector under Scenario 2 (MT)

Assessment of Potential Impacts of HFO-1234yf and TFA

This section uses the projected emissions of HFO-1234yf described in
section   REF _Ref215975691 \r \h  \* MERGEFORMAT  4  to predict impacts
on aquatic communities, soils and plants, and local air quality. 
Emissions from each scenario for the year 2050 were scaled from the
national emissions estimates according to population for Houston and Los
Angles regions to determine reasonable worst-case impacts.  These
regions were chosen based on the potential presence of vernal pools,
their susceptibility to high TFA deposition concentrations, and their
continuing and chronic problem with high levels of ground level ozone.

Using EPA’s CMAQ model version 4.7, a one-year simulation was
performed using 2001 meteorological data to project maximum monthly TFA
rainwater concentrations, monthly maximum dry deposition of TFA, and
maximum 8-hr ozone concentrations for the Los Angeles and Houston
regions resulting from emissions of HFO-1234yf from those regions only. 
The model used the extended version of the carbon bond five chemical
mechanism as developed by Luecken et al. (2010), which incorporates the
gaseous and aqueous chemistry of HFO-1234yf and its products.  The
results from this analysis are described in the remainder of this
section.

TFA Rainwater Concentrations

Monthly maximum average TFA rainwater concentrations for each region
under each scenario are summarized in   REF _Ref260304976 \h  Table 7 .

Table   SEQ Table \* ARABIC  7 : Summary of Estimated Monthly Average
TFA Rainwater Concentrations in 2050 (ng/L)

Region	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec

Scenario 1

Los Angeles	90	32	166	167.	969	1116	707	944	170	120	196	94

Houston	18	21	32	34	50	75	106	59	54	19	16	27

Scenario 2

Los Angeles	174	63	322	322	1475	1700	1077	1438	319	232	380	182

Houston	35	40	61	51	76	114	161	90	85	37	30	51

Under scenario 1, the results indicate that the maximum monthly average
TFA rainwater concentration in the Los Angeles region in 2050 is 1,116
ng/L, while the maximum monthly average TFA rainwater concentration in
the Houston region in 2050 is 106 ng/L.  Under scenario 2, the results
indicate that the maximum monthly average TFA rainwater concentration in
the Los Angeles region in 2050 is 1,700 ng/L, while the maximum monthly
average TFA rainwater concentration in the Houston region in 2050 is 161
ng/L.  

For Los Angeles, June represents the month with the highest projected
monthly average TFA rainwater concentration, while for Houston, July
represents the month with the highest projected monthly average TFA
rainwater concentration.  The monthly average maximum TFA rainwater
concentrations for these two peak months are geographically depicted
below in   REF _Ref260395334 \h  \* MERGEFORMAT  Figure 3  and   REF
_Ref260395338 \h  \* MERGEFORMAT  Figure 4 , for both scenarios, for Los
Angeles and Houston, respectively.  

 Figure   SEQ Figure \* ARABIC  3 : June 2050 Los Angeles Scenario 1 and
Scenario 2 Results 

Figure   SEQ Figure \* ARABIC  4 : July 2050 Houston Scenario 1 and
Scenario 2 Results 

TFA Dry Deposition

  REF _Ref260387062 \h  Table 8  presents the results of both the
maximum annual and monthly maximum TFA deposition expressed on an annual
basis.  

Table   SEQ Table \* ARABIC  8 : Summary of Estimated TFA Dry Deposition
in 2050 

	Annualized TFA Maximum 

Monthly Average Flux Ratea 	TFA Maximum 

Annual Average Flux Rate

	nmole/m2-yr	(g/m2-yr	nmole/m2-yr	(g/m2-yr

Scenario 1

Los Angeles	15,252	566	3,838	143

Houston	2,556	95	934	35

Scenario 2

Los Angeles	23,232	863	6,393	237

Houston	3,912	145	1,551	58

Notes:  Formula weight of TFA is 114 g/mole. 

a Maximum concentration occurred in May for Los Angeles and in July for
Houston.  Results are expressed on annual basis using the peak monthly
deposition rate times 12. 

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
this part of the state compared to other geographical areas of the
United States.  For comparison, measured TFA flux rates from two vernal
pool systems outside of Sacramento, California are presented in   REF
_Ref226341580 \h  Table 9  (Cahill et al. 2001; data taken in 1998 and
1999).

Table   SEQ Table \* ARABIC  9 : TFA Measurements in California Vernal
Pools, 1998-1999

Observed Year	Flux Rate Values Measured in California Vernal Pools

	ng/m2-day	(g/m2-yr

1998-1999	134*	49

1998-1999	110**	40

1998-1999	152***	56

Notes:  Values of (g/m2-yr = ng/m2-day * 365 days/1000.

*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.

The values above indicate that projected maximum annual average
deposition of TFA will be somewhat greater than what has been measured
in vernal pools in the last decade in Northern California.  For Southern
California, measured values in vernal pools would be expected to be
somewhat higher than those reported owing to the reduced rainfall
compared to Northern California. 

Ground Level Ozone Concentrations

Under scenario 1, results for the Los Angeles region show a maximum
increase in the 8-hr ozone concentration of 0.053 ppb, while results for
the Houston region show a maximum increase in the 8-hr ozone
concentration of 0.014 ppb.  Under scenario 2, results for the Los
Angeles region show a maximum increase in the 8-hr ozone concentration
of 0.080 ppb, while results for the Houston region show a maximum
increase in the 8-hr ozone concentration of 0.021 ppb.  Maximum
increases in 8-hr ozone concentrations under each scenario are
geographically depicted in   REF _Ref260308122 \h  \* MERGEFORMAT 
Figure 5  and   REF _Ref260309321 \h  \* MERGEFORMAT  Figure 6  below. 
REF _Ref260308128 \h  \* MERGEFORMAT  

  

Figure   SEQ Figure \* ARABIC  5 : LA May 22, 2050 Scenario 1 and
Scenario 2 Results

Figure   SEQ Figure \* ARABIC  6 : Houston June 11, 2050 Scenario 1 and
Scenario 2 Results

Discussion of Results

The following section provides a summary of the findings described in
section 5 and additionally provides an overview of the limitations of
this analysis.

In section 3.1 of this paper, based on available studies, it was
concluded that the NOEC is 0.12 mg/L (120,000 ng/L) for freshwater green
algae, 10 mg/L (10,000,000 ng/L) for vernal pool microbial species, and
1 mg/L (1,000,000 ng/L) for vernal pool plant species.  Relative to
these levels, in the worst case scenario, TFA rainwater concentrations
are expected to reach 1,116 ng/L in 2050, well below the NOEC of
1,000,000 ng/L for vernal pool species.  The measured concentration of
TFA in rainwater is only ten times greater than the 2020 level of TFA in
rainwater projected from the current rate of production from atmospheric
degradation of HFCs and HCFCs, which is estimated to be almost 0.0001
mg/L or 100 ng/L  (Berends et al. 1999), but still 1,000 times lower
than the NOEC for tested vernal pool species.  

NOECs are 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 that less dilution is expected in vernal pools and
similar seasonal water bodies that have no significant outflow capacity.
 

Although dry deposition of TFA in vernal pools has been projected to
potentially be almost five times greater than concentrations measured in
1998-1999, studies indicate that vernal pools species are unlikely to be
harmed because plant and animal species tested to date do not
bioconcentrate TFA and the compound has not been shown to affect plant
germination rates.  It is noted that no NOEC values have been identified
based solely on dry deposition of TFA, or on a combined wet/dry
deposition model, but it is not expected that there will be adverse
impacts based on the lack of reported bioconcentration and germination
effects.

In regards to ground level ozone formation, based on the findings
described in section 5.3 and assuming an 8-hr ozone standard of 75 ppb,
HFO-1234yf is projected to contribute to a maximum of roughly 0.07% -
0.1% and 0.02% - 0.03% of total ground-level ozone in Los Angeles and
Houston, respectively.  These percentage increases are presented
relative to the proposed 75 ppb standard for ozone, although it is
unclear what the standard will be in the future with possible changes 
in standards for emissions of criteria pollutants, VOCs, and NOx.  

Summary of Findings

Based on results presented above, certain 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 a potential 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. Current risk
assessments, though, indicate this is not a significant concern. 

 

Non-attainment resulting from HFO-1234yf emissions is not likely to be a
concern for local air quality in all locations. HFO-1234yf could
potentially increase ground level ozone by up to 0.1% in the most
extreme case.   Given the expected photochemical reactivity of
HFO-1234yf, emissions of HFO-1234yf are not expected to significantly
result in ground level ozone formation.

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. 

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.

Aquatic and Soil Impacts

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 and marine flora and fauna in the screening tests.  These
plant and animal species, however, with the possible exception of
Daphnia magna, and some algal species, are not typical of specialized
vernal pool species in California such as meadow foam, Downingia,
Navarettia, fairy shrimp, tadpole shrimp, and 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. However, one study (Benesch et
al. 2002) did look at vernal pool microbial and plant species and found
that predicted TFA concentrations would not adversely affect these
receptors.  Further, current and predicted TFA concentrations are well
below effect levels in many related ecological receptors, and lower
aquatic life forms do not bioconcentrate TFA.  These data indicate that
despite full knowledge of the effects of TFA on vernal pool species,
adverse ecological effects are not anticipated.

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.

Air Quality 

Improvements in the understanding of the reactivity of HFO-1234yf and
resulting production of TFA and ozone formation have potential 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 affect the precursor ozone emissions.  For
example, EPA recently finalized a rule for a new 1-hour NO2 standard in
the range between 80 to 100 ppb.  In order to meet future standards,
significant 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.

References

1234yf OEM Group. 2008. MAC Summit 2008.  Available at
<http://www.epa.gov/cppd/mac/HFO1234YF%20EXPERT%20CONSENSUS%20GROUP.ppt>

Abstracts: South African Association of Botanists – Annual meeting
2006. South African Journal of Botany 72:313-347

Benesch JA, MS Gustin, GR Cramer, and TM Cahill. 2002. Investigation of
effects of trifluoroacetate on vernal pool ecosystems.  Environ Toxicol
and Chem. 21(3):640-47.

Berends, AG, JC Boutonnet, C de Rooij, and RS Thompson.  1999. Toxicity
of Trifluoroacetate to Aquatic Systems. Environ Toxicol Chem. 
18(5):1053–1059. 

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2067–2082.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	-	-	39	7	46

2011	-	-	111	20	132

2012	-	-	218	40	258

2013	-	-	361	66	426

2014	-	-	541	98	640

2015	-	-	762	138	900

2016	407	407	1,093	196	1,696

2017	1,229	1,229	1,541	273	3,043

2018	2,472	2,472	2,110	369	4,951

2019	4,143	4,143	2,807	485	7,435

2020	6,244	6,244	3,636	620	10,501

2021	8,332	8,332	4,487	766	13,585

2022	10,413	10,413	5,389	916	16,718

2023	12,513	12,513	6,278	1,066	19,857

2024	14,644	14,644	7,209	1,216	23,069

2025	16,812	16,812	8,128	1,367	26,307

2026	19,003	19,003	9,043	1,516	29,561

2027	21,203	21,203	9,953	1,678	32,834

2028	23,962	23,962	10,914	1,848	36,724

2029	26,335	26,335	11,817	2,017	40,170

2030	28,327	28,327	12,748	2,221	43,296

2031	29,926	29,926	13,591	2,412	45,929

2032	31,118	31,118	14,348	2,577	48,043

2033	31,295	31,295	14,918	2,720	48,932

2034	31,514	31,514	15,479	2,861	49,854

2035	31,791	31,791	15,924	3,010	50,725

2036	32,084	32,084	16,382	3,213	51,678

2037	32,374	32,374	16,824	3,408	52,606

2038	32,627	32,627	17,249	3,592	53,468

2039	32,857	32,857	17,656	3,767	54,280

2040	33,093	33,093	18,046	3,931	55,070

2041	33,345	33,345	18,371	4,008	55,724

2042	33,637	33,637	18,668	4,080	56,385

2043	33,906	33,906	18,921	4,151	56,977

2044	34,177	34,177	19,156	4,217	57,549

2045	34,450	34,450	19,374	4,278	58,102

2046	34,726	34,726	19,566	4,315	58,606

2047	35,004	35,004	19,756	4,351	59,110

2048	35,284	35,284	19,944	4,383	59,611

2049	35,566	35,566	20,132	4,415	60,112

2050	35,851	35,851	20,318	4,447	60,616

* 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 v4.4_12-16-09.   

 ICF International. 2009. Assessment of the Potential Impacts of
HFO-1234yf and the Associated Production of Trifluoroacetic Acid (TFA)
on Aquatic Communities and Local Air Quality. Prepared by ICF
International for U.S. EPA. July 31, 2009.  Available online at  
HYPERLINK "http://www.regulations.gov"  www.regulations.gov  in docket
ID: EPA-HQ-OAR-2008-0664-0037.

 More information is available on the CMAQ model at   HYPERLINK
"http://cmascenter.org/"  http://cmascenter.org/ .

 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.

 Research sponsored by the Alternative Fluorocarbons Environmental
Acceptability Study (AFEAS) and conducted by independent scientists at
universities, private research organizations, and government
laboratories.

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

.

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

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

	                                                      	  TFA Assessment

 PAGE   

	                                                      	  TFA Assessment

	                                                      	  TFA Assessment

 PAGE   1 

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 PAGE   ii 

 PAGE   1 

      100-year GWPs of Selected HCFCs and HFCs 

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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)

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

Chemical and Physical Properties of TFA

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