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6560-50-P

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 51

[EPA-HQ-OAR-2010-0605; FRL- ]

RIN 2060-AQ38

Air Quality: Revision to Definition of Volatile Organic Compounds –

Exclusion of trans-1,3,3,3-tetrafluoropropene and 2,3,3,3-

tetrafluoropropene

AGENCY: Environmental Protection Agency (EPA). 

ACTION: Proposed rule.

SUMMARY: The EPA is proposing to revise the agency’s definition of 

volatile organic compounds (VOCs) for purposes of preparing state 

implementation plans (SIPs) to attain the national ambient air 

quality standards (NAAQS) for ozone under Title I of the Clean Air 

Act (CAA). This proposed revision would add 2,3,3,3-

tetrafluoropropene (also known as HFO-1234yf) and trans-1,3,3,3-

tetrafluoropropene (also known as HFO-1234ze) to the list of 

compounds excluded from the definition of VOC on the basis that these 

compounds make a negligible contribution to tropospheric ozone 

formation. 

DATES: Comments must be received on or before [INSERT DATE 30 DAYS 

AFTER PUBLICATION IN THE FEDERAL REGISTER]. 

Public Hearing: If anyone contacts us requesting to speak at a 

public hearing on or before [INSERT DATE 15 DAYS AFTER PUBLICATION IN 

THE FEDERAL REGISTER], we will hold a public hearing. Additional 
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information about the hearing would be published in a subsequent 

Federal Register notice.

ADDRESSES: Submit your comments, identified by Docket ID No. EPAHQ-OAR-2010-0605, by one of the following methods:

 www.regulations.gov. Follow the on-line instructions for 

submitting comments.

 Email: a-and-r-Docket@epamail.epa.gov, Attention Docket ID No. 

EPA-HQ-OAR-2010-0605.

 Fax: 202-566-1541, Attention Docket ID No. EPA-HQ-OAR-2010-

0605.

 Mail: Docket ID No. EPA-HQ-OAR-2010-0605, Environmental 

Protection Agency, Mailcode: 6102T, 1200 Pennsylvania Ave., NW, 

Washington, D.C. 20460.

 Hand Delivery: EPA Docket Center, U.S. Environmental Protection 

Agency, 1301 Constitution Avenue, NW, Room: 3334, Mail Code: 

6102T, Washington, D.C. 20460, Attention Docket ID No. EPA-HQOAR-2010-0605. Such deliveries are only accepted during the 

Docket’s normal hours of operation, and special arrangements 

should be made for deliveries of boxed information.

Instructions: Direct your comments to Docket ID No. EPA-HQ-OAR-2010-

0605. The EPA's policy is that all comments received will be included 

in the public docket without change and may be made available online 

at www.regulations.gov, including any personal information provided, 

unless the comment includes information claimed to be Confidential 
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Business Information (CBI) or other information whose disclosure is 

restricted by statute. Do not submit information that you consider to 

be CBI or otherwise protected through www.regulations.gov, or email. 

The www.regulations.gov website is an “anonymous access” system, 

which means the EPA will not know your identity or contact 

information unless you provide it in the body of your comment. If you 

send an email comment directly to the EPA without going through 

www.regulations.gov, your email address will be automatically 

captured and included as part of the comment that is placed in the 

public docket and made available on the Internet. If you submit an 

electronic comment, the EPA recommends that you include your name and 

other contact information in the body of your comment and with any 

disk or CD-ROM you submit. If the EPA cannot read your comment due to 

technical difficulties and cannot contact you for clarification, the 

EPA may not be able to consider your comment. Electronic files should 

avoid the use of special characters, any form of encryption, and be 

free of any defects or viruses. For additional information about the

EPA’s public docket, visit the EPA Docket Center homepage at 

http://www.epa.gov/epahome/dockets.htm.

Docket: All documents in the docket are listed in the 

www.regulations.gov index. Although listed in the index, some 

information is not publicly available, i.e., CBI or other information 

whose disclosure is restricted by statute. Certain other material, 

such as copyrighted material, will be publicly available only in hard 
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copy. Publicly available docket materials are available either 

electronically in www.regulations.gov or in hard copy at the EPA, 

EPA/DC, EPA West, Room 3334, 1301 Constitution Ave., NW, Washington, 

D.C. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., 

Monday through Friday, excluding legal holidays. The telephone number 

for the Public Reading Room is (202) 566-1744, and the telephone 

number for the EPA Docket is (202) 566-1742. 

FOR FURTHER INFORMATION CONTACT: David Sanders, Office of Air 

Quality Planning and Standards, Air Quality Policy Division, Mail 

Code C539-01, Research Triangle Park, NC 27711; telephone: (919) 541-

3356; fax number: (919) 541-0824; email address: 

sanders.dave@epa.gov.

SUPPLEMENTARY INFORMATION: 

I. General Information

A. Does this action apply to me?

Entities potentially affected by this proposed rule include, but 

are not necessarily limited to, states (typically state air pollution 

control agencies) that control VOCs, and industries involved in the 

manufacture or use of refrigerants, aerosol propellants, and blowing 

agents for insulating foams.

Industry group SICa NAICSb

Refrigerants

Aerosol propellants

Blowing agents

2869, 3585

2869

2869, 3086 

238220, 336111, 336391

325998

326140, 326150
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a Standard Industrial Classification.

b North American Industry Classification System.

This proposed rule is applicable to all manufacturers, 

distributors, and users of these chemical compounds. The use of these 

compounds is subject to restrictions under the CAA and the Toxic 

Substances Control Act (TSCA). Specifically, the use of these 

compounds as aerosol propellants, blowing agents, or refrigerants, or 

any other use in which they would substitute for chlorofluorocarbons, 

hydrochlorofluorocarbons, or their substitutes, is subject to 

restrictions under the Significant New Alternatives Policy (SNAP) 

program (CAA §612; 40 CFR 82 subpart G). The SNAP program has issued 

a final approval for HFO-1234yf as a substitute for use in the motor 

vehicle air conditioning end-use as a replacement for ozone depleting 

substances (76 FR 17488, March 29, 2011), and final approvals for 

HFO-1234ze as a suitable foam and refrigerant substitute and as a 

propellant (74 FR 50129, September 30, 2009; 75 FR 34017, June 16, 

2010). Furthermore, HFO-1234yf is subject to a Significant New Use 

Rule (SNUR) under TSCA. (75 FR 65987, October 27, 2010). The 

implications of these other regulations are discussed in more detail 

in Section III. 

B. What should I consider as I prepare my comments for the EPA?

Submitting CBI: Do not submit this information to the EPA 

through www.regulations.gov or email. Clearly mark the part or all of 

the information that you claim to be CBI. For CBI information in a 

disk or CD ROM that you mail to the EPA, mark the outside of the disk 
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or CD ROM as CBI and then identify electronically within the disk or 

CD ROM the specific information that is claimed as CBI. In addition 

to one complete version of the comment that includes information 

claimed as CBI, a copy of the comment that does not contain the 

information claimed as CBI must be submitted for inclusion in the 

public docket. Information so marked will not be disclosed except in 

accordance with procedures set forth in 40 CFR part 2. 

C. How can I find information about a possible public hearing? 

Public Hearing: To request a public hearing or information 

pertaining to a public hearing on this document, contact Ms. Pamela 

S. Long, Air Quality Policy Division, Mail code C504-01, U.S. 

Environmental Protection Agency, Research Triangle Park, NC 27711, 

telephone (919) 541-0641, facsimile number (919) 541-5509, email

address: long.pam@epa.gov. 

D. How is this preamble organized? 

The information presented in this preamble is organized as follows:

I. General Information

A. Does this action apply to me?

B. What should I consider as I prepare my comments for the EPA?

C. How can I find information about a possible public hearing?

D. How is this preamble organized?

II. Background

A. Petition to list HFO-1234yf

B. Petition to list HFO-1234ze

III. The EPA’s Proposed Responses to the Petitions

A. Contribution to Tropospheric Ozone

B. Likelihood of Risk to Human Health or the Environment

C. Conclusions

IV. Proposed Action

V. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Executive

Order 13563: Improving Regulation and Regulatory Review
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B. Paperwork Reduction Act

C. Regulatory Flexibility Act

D. Unfunded Mandates Reform Act

E. Executive Order 13132: Federalism

F. Executive Order 13175: Consultation and Coordination with 

Indian Tribal Governments

G. Executive Order 13045: Protection of Children from 

Environmental Health and Safety Risks

H. Executive Order 13211: Actions that Significantly Affect 

Energy Supply, Distribution, or Use

I. National Technology Transfer and Advancement Act 

J. Executive Order 12898: Federal Actions to Address 

Environmental Justice in Minority Populations and Low-Income 

Populations.

II. Background

Tropospheric ozone, commonly known as smog, is formed when VOCs 

and nitrogen oxides (NOx) react in the atmosphere in the presence of 

sunlight. Because of the harmful health effects of ozone, the EPA and 

state governments limit the amount of VOCs that can be released into 

the atmosphere. The VOCs are those organic compounds of carbon which 

form ozone through atmospheric photochemical reactions. Different 

VOCs have different levels of reactivity -- that is, they do not 

react to form ozone at the same speed or do not form ozone to the

same extent. Some VOCs react slowly, or form less ozone; therefore,

changes in their emissions have limited effects on local or regional 

ozone pollution episodes. It has been the EPA’s policy that organic 

compounds with a negligible level of reactivity should be excluded 

from the regulatory definition of VOC so as to focus VOC control 

efforts on compounds that do significantly increase ozone 

concentrations. The EPA also believes that exempting such compounds 

creates an incentive for industry to use negligibly reactive 
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compounds in place of more highly reactive compounds that are 

regulated as VOCs. The EPA lists these negligibly reactive compounds 

in its regulations (at 40 CFR 51.100(s)) and excludes them from the 

definition of VOC. 

The CAA requires the regulation of VOCs for various purposes. 

Section 302(s) of the CAA specifies that the EPA has the authority to 

define the meaning of “VOC,” and hence what compounds shall be 

treated as VOCs for regulatory purposes. The policy of excluding 

negligibly reactive compounds from the VOC definition was first laid 

out in the “Recommended Policy on Control of Volatile Organic 

Compounds” (42 FR 35314, July 8, 1977) and was supplemented most 

recently with the “Interim Guidance on Control of Volatile Organic 

Compounds in Ozone State Implementation Plans” (Interim Guidance)(70 

FR 54046, September 13, 2005). The EPA uses the reactivity of ethane 

as the threshold for determining whether a compound has negligible 

reactivity. Compounds that are less reactive than, or equally 

reactive to, ethane under certain assumed conditions may be deemed 

negligibly reactive and therefore suitable for exemption from the 

regulatory definition of VOC. Compounds that are more reactive than 

ethane continue to be considered VOCs for regulatory purposes and 

therefore subject to control requirements. The selection of ethane as 

the threshold compound was based on a series of smog chamber 

experiments that underlay the 1977 policy. 
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The EPA has used three different metrics to compare the 

reactivity of a specific compound to that of ethane: (i) the 

reaction rate constant (known as kOH) with the hydroxyl radical (OH);

(ii) the maximum incremental reactivities (MIR) of ethane and the 

compound in question expressed on a reactivity per unit mass basis; 

and (iii) the MIR of ethane and the compound in question expressed on 

a reactivity per mole basis. Differences between these three metrics 

are discussed below. 

The kOH is the reaction rate constant of the compound with the OH 

radical in the air. This reaction is typically the first step in a 

series of chemical reactions by which a compound breaks down in the 

air and participates in the ozone-forming process. If this step is 

slow, the compound will likely not form ozone at a very fast rate. 

The kOH values have long been used by the EPA as a measure of 

photochemical reactivity and ozone-forming activity, and they have 

been the basis for most of the EPA’s previous exemptions of 

negligibly reactive compounds from the regulatory definition of VOC. 

The kOH metric is inherently a molar comparison, i.e., it measures the 

rate at which molecules react.

The MIR values, both by mole and by mass, are a more recently 

developed measure of photochemical reactivity derived from a 

computer-based photochemical model. This measurement considers the 

complete ozone forming activity of a compound, not merely the first 

reaction step. Further explanation of the MIR metric can be found in: 
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W. P. L. Carter, “Development of Ozone Reactivity Scales for Volatile 

Organic Compositions,” Journal of the Air & Waste Management 

Association, Vol. 44, 881-899, July 1994.

The MIR values for compounds are typically expressed as grams of 

ozone formed per gram of VOC (mass basis), but may also be expressed 

as grams of ozone formed per mole of VOC (molar basis). For comparing 

the reactivities of two compounds, using the molar MIR values 

considers an equal number of molecules of the two compounds. 

Alternatively, using the mass MIR values compares an equal mass of 

the two compounds, which will involve different numbers of molecules, 

depending on the relative molecular weights. The molar MIR comparison 

is consistent with the original smog chamber experiments that 

underlie the original selection of ethane as the threshold compound

and compared equal molar concentrations of individual VOCs. It is 

also consistent with previous reactivity determinations based on 

inherently molar kOH values. By contrast, the mass MIR comparison is 

more consistent with how MIR values and other reactivity metrics have 

been applied in reactivity-based emission limits, such as the 

national VOC emissions standards for aerosol coatings (73 FR 15604).

Many other VOC regulations contain limits based upon a weight of VOC 

per volume of product, such as the EPA’s regulations for limiting VOC 

emissions from architectural and industrial maintenance coatings (65 

FR 7736). However, the fact that regulations are structured to 

measure VOC content by weight for ease of implementation and 
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enforcement does not necessarily control whether VOC exemption 

decisions should be made on a weight basis as well.

The choice of the molar basis versus the mass basis for the 

ethane comparison can be significant. Given the relatively low 

molecular weight of ethane, use of the mass basis tends to result in 

more VOCs being classified as “negligibly reactive” than in the case 

of the molar basis. In some cases, a compound might be considered 

less reactive than ethane and eligible for VOC exemption under the 

mass basis but not under the molar basis. The compounds considered in 

this proposal, HFO-1234yf and HFO-1234ze, fall into this category, 

where the molar MIR value is greater than that of ethane, but the 

mass MIR value is equal to or less than that of ethane. However, for 

both compounds, both MIR values fall in the lower portion of the very 

wide range of VOC reactivities. 

The EPA has considered the choice between a molar or mass basis 

for the comparison to ethane in past rulemakings and guidance. Most 

recently, in the Interim Guidance, the EPA stated:

[A] comparison to ethane on a mass basis strikes the right 

balance between a threshold that is low enough to capture 

compounds that significantly affect ozone concentrations and a 

threshold that is high enough to exempt some compounds that may 

usefully substitute for more highly reactive compounds.

When reviewing compounds that have been suggested for VOC-exempt 

status, EPA will continue to compare them to ethane using kOH

expressed on a molar basis and MIR values expressed on a mass 

basis.

In this action, the EPA is proposing to exempt these compounds 

using the comparison to ethane on the mass basis MIR value, because 
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MIR values are available for these compounds and the EPA believes 

that this comparison is appropriate.

The EPA’s 2005 Interim Guidance also notes that concerns have 

sometimes been raised about the potential impact of a VOC exemption 

on environmental endpoints other than ozone concentrations, including 

fine particle formation, air toxics exposures, stratospheric ozone 

depletion, and climate change. The EPA has recognized, however, that 

there are existing regulatory and non-regulatory programs that are 

specifically designed to address these issues, and the agency 

continues to believe that the impacts of VOC exemptions on 

environmental endpoints other than ozone formation will be adequately 

addressed by these programs. The VOC exemption policy is intended to 

facilitate attainment of the ozone NAAQS, and questions have been 

raised as to whether the agency has authority to use its VOC 

exemption policy to address concerns that are unrelated to groundlevel ozone. Thus, in general, VOC exemption decisions will continue 

to be based solely on consideration of a compound's contribution to 

ozone formation. However, if the agency determines that a particular 

VOC exemption is likely to result in a significant increase in the 

use of a compound and that the increased use would pose a significant 

risk to human health or the environment that would not be addressed 

adequately by existing programs or policies, the EPA reserves the

right to exercise its judgment in deciding whether to grant an 

exemption. 
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In this case, the agency has examined available information on 

the risks to human health and the environment and applicability of 

other regulatory programs; that information for the two compounds

considered here is discussed further in Section III.

A. Petition to list HFO-1234yf

Honeywell, Inc. submitted a petition to the EPA on June 29, 

2009, requesting that HFO-1234yf (CAS 754-12-1) be exempted from VOC 

control based on its low reactivity relative to ethane. The 

petitioner indicated that HFO-1234yf may be used as a refrigerant for 

refrigeration and air-conditioning. Honeywell also indicated that it 

expects HFO-1234yf to be widely used as a replacement for HFC-134a in 

motor vehicle air-conditioners (MVAC), and that HFO-1234yf has been 

specifically developed for this purpose. Honeywell argues that as a 

replacement for use in motor vehicle air conditioners there will be 

an environmental advantage in that the global warming potential (GWP) 

of HFO-1234yf is 4, which is substantially lower than the GWP for 

HFC-134a (100-year GWP = 1430) which HFO-1234yf is designed to 

replace. Honeywell submitted several documents, including several 

peer-reviewed journal articles, to support this petition that have 

been added to the docket for this action.

B. Petition to list HFO-1234ze 

Honeywell, Inc. also submitted a petition to the EPA on December 

2, 2009, requesting that HFO-1234ze (CAS 29118-24-9) be exempted from 

VOC control based on its low reactivity relative to ethane. The 
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petitioner indicated that HFO-1234ze may be used in a variety of 

applications including as a refrigerant, an aerosol propellant, and a 

blowing agent for insulating foam. Honeywell submitted several 

documents, including several peer-reviewed journal articles, to 

support its petition, all of which have been added to the docket for 

this action. 

III. The EPA’s Proposed Responses to the Petitions

Consistent with the Interim Guidance, the EPA’s proposed 

responses to the petitions are based on a consideration of the 

contribution that each chemical makes to tropospheric ozone formation 

based on a comparison of reactivity metrics, and our assessment that

existing programs or policies already adequately address the 

possibility that granting each petition would pose a significant risk 

to human health or the environment. We also believe that the much 

lower global warming potential of HFO-1234yf compared to the compound 

HFC-134a for which it will substitute, as described in Section III.B, 

is an additional reason to approve the HFO-1234yf petition in 

particular, given that applying the Interim Guidance itself supports 

such approval. Information on these topics is given below. 

A. Contribution to Tropospheric Ozone

Table 1 presents three reactivity metrics for ethane (the 

benchmark compound) and for HFO-1234yf and HFO-1234ze which are 

proposed for exemption from the VOC definition in this proposed rule. 

Table 1 - Reactivities of ethane, HFO-1234ze and 
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HFO-1234yf

Compound kOH

(cm3/moleculesec)

MIR 

(g O3/mole

VOC)

MIR 

(g O3/gram

VOC)

Ethane 2.4 x 10-13 8.4 0.28

HFO-1234yf 10.5 x 10-13 31.92 0.28

HFO-1234ze 9.25 x 10-13 11.2 0.098

Notes:

1. kOH value for ethane is from: R. Atkinson., D. L. Baulch, R. A. 

Cox, J. N. Crowley, R. F. Hampson, Jr., R. G. Hynes, M. E. 

Jenkin, J. A. Kerr, M. J. Rossi, and J. Troe (2004), Summary of 

evaluated kinetic and photochemical data for atmospheric 

chemistry. 

2. kOH value for HFO-1234ze is from: R. Sondergaard, O. J. Nielsen, 

M. D. Hurley, T. J. Wallington, and R. Singh, “Atmospheric 

chemistry of trans-CF3CH=CHF: kinetics of the gas-phase 

reactions with Cl atoms, OH radicals, and O3.” Chemical Physics 

Letters, 443 (2007) 199-204.

3. kOH value for HFO-1234yf is from: O.J. Nielson, M.S. Javadi, 

M.P. Sulbaek Anderson, M.D. Hurley, T.J. Wallington, R. Singh,

“Atmospheric Chemistry of CF3CF=CH2: kinetics and mechanisms of 

gas-phase reactions with Cl atoms, OH Radicals, and O3,” Chemical 

Physical Letters, 439 (2007) 18-22.

4. Maximum incremental reactivity or MIR (g O3/g VOC) values of 

ethane, HFO-1234ze and HFO-1234yf are from: William P. L. 

Carter, “Development of the SAPRC-07 chemical mechanism and 

updated ozone reactivity scales” (updated 1/27/10).

http://www.engr.ucr.edu/~carter/SAPRC/saprc07.pdf. 

5. Molar MIR (g O3/mole VOC) values were calculated from the mass 

MIR (g O3/g VOC) values by determining the number of moles per 

gram of the relevant organic compound.

From the data in Table 1, it can be seen that HFO-1234yf has a 

higher kOH value than ethane, meaning that it initially reacts more 

quickly in the atmosphere than ethane. A molecule of HFO-1234yf is 

also more reactive than a molecule of ethane, as shown by the molar 
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MIR (g O3/mole VOC) values, because equal numbers of moles have equal 

numbers of molecules. However, a gram of HFO-1234yf has the same 

reactivity as a gram of ethane. This is because HFO-1234yf has a 

molecular weight (114) that is more than three times that of ethane 

(molecular weight 30), and thus requires less than a third the number 

of molecules of HFO-1234yf per gram than the number of molecules of 

ethane per gram.

From the data in Table 1, it also can be seen that HFO-1234ze

has a higher kOH value than ethane, meaning that it initially reacts 

more quickly in the atmosphere than ethane. A molecule of HFO-1234ze

is also more reactive than a molecule of ethane, as shown by the 

molar MIR (g O3/mole VOC) values, since equal numbers of moles have 

equal numbers of molecules. However, a gram of HFO-1234ze is less 

reactive, or creates less ozone on the day of its emission to the 

atmosphere, than a gram of ethane. This is because HFO-1234ze has a 

molecular weight (114) that is more than three times that of ethane 

(molecular weight 30), and thus requires less than a third the number 

of molecules of HFO-1234ze per gram than the number of molecules of 

ethane needed per gram. 

Thus, for both of the petitions submitted by Honeywell, the data 

supports the contention that the reactivity of the compound in the 

petition is equal to or lower than that of ethane on a mass MIR 

basis.
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We anticipate that one of these compounds, HFO-1234yf, will be 

used in automobiles as a replacement for the current refrigerant HFC134a, which is the only use for which HFO-1234yf has been approved to 

date under the SNAP program. Given this one-for-one substitution 

situation, it is informative to compare the ozone forming potential 

of HFO-1234yf to that of HFC-134a, which has a gram MIR of only 

0.0007 and thus contributes very little to ozone formation. The EPA 

has considered the results of a recent peer-reviewed study of the 

increase in ozone that may occur as result of the substitution of 

HFO-1234yf for HFC-134a.2 Based on air quality modeling, this study 

found that if HFO-1234yf was used in all automobiles but not in any 

other application, the incremental amount of ozone formed from its 

degradation in the atmosphere was only 0.01% of total ozone formed 

during the simulation due to emissions from all sources. This portion 

of ozone formation due to automobiles is slightly more than the 

current baseline, where the refrigerant used is HCF-134a.

3 Thus, the 

additional information from this study shows that, under the 

assumptions used in the air quality modeling, the use of HFO-1234yf

would produce more ozone than continued use of HFC-134a, but the 

 

2

 D. Luecken, R. Waterland, S. Papasavva, K. Taddonio, W. Hutzell, J. 

Rugh, and S. Andersen. Ozone and TFA Impacts in North America from 

Degradation of 2,3,3,3-Tetrafluoropropene (HFO-1234yf), A Potential 

Greenhouse Gas Replacement. Environ. Sci. Technol. 44, pp. 343-349.

3

 The study also noted that if 2,3,3,3-tetrafluoropropene were used 

in additional applications that are currently not legal in the U.S, 

e.g., non-vehicle refrigerant applications, its contribution to ozone 

formation would be greater, but did not quantify this potential 

contribution.
Page 18 of 32

increase is unlikely to have a significant impact on local air 

quality. One of the assumptions used in the modeling was that the 

substitution of one refrigerant for the other would not affect 

meteorological conditions that also influence ozone formation.

However, as stated in Section II.A, HFO-1234yf has a much lower 

GWP than HFC-134a. Global warming is predicted to exacerbate high 

ozone concentrations4,5, so directionally the lower GWP of HFO-1234yf

will offset at least some of the ozone increase predicted by the 

modeling that assumed identical meteorological conditions. The EPA 

believes the very small increase in ozone concentrations that may 

result from encouraging the use of HFO-1234yf via an exemption from 

the definition of VOC does not constitute a sufficient reason to 

depart from the Interim Guidance’s reliance on MIR comparisons to 

ethane as the basis for approving VOC exemption requests.

In summary, for both HFO-1234yf and HFO-1234ze, the EPA believes 

that these chemicals qualify as negligibly reactive with respect to 

their contribution to tropospheric ozone formation.

B. Likelihood of Risk to Human Health or the Environment

Additionally, we examined and present available information on 

the likelihood of risk to human health or the environment from 

 

4

 U.S. EPA. Assessment of the Impacts of Global Change on Regional 

U.S. Air Quality: A Synthesis of Climate Change Impacts on GroundLevel Ozone (An Interim Report of the U.S. EPA Global Change Research 

Program). U.S. Environmental Protection Agency, Washington, D.C., 

EPA/600/R-07/094F, 2009.

5 Jacob, Daniel J. and Darrell A. Winner (2009). Effect of climate 

change on air quality, Atmospheric Environment, 43:51-63.
Page 19 of 32

increased use of the chemicals considered here. We believe that 

current regulation of these compounds under other EPA programs

adequately protects human health and the environment.

The only currently known or potential uses for the chemicals

being considered here are as substitutes for stratospheric ozonedepleting substances (ODS), and any such use is regulated under the 

SNAP program. Under SNAP, the EPA reviews all new substitutes for ODS

and allows their use in specific applications where the overall risks 

to human health and the environment associated with their use are 

comparable to or less than those of other compounds used in the same 

manner. 

After reviewing available information and public comments 

regarding its safety, health, and environmental risks and benefits 

under the SNAP program, the EPA issued a final approval on March 29, 

2011 (76 FR 174888) for HFO-1234yf as an acceptable ODS substitute 

for use in MVAC, subject to specific use conditions, in place of CFC12 and HFC-134a.

6 The use conditions in the SNAP approval have the 

effect of making it illegal to use HFO-1234yf in the air conditioning 

systems of heavy-duty trucks, refrigerated transport, or off-road 

vehicles such as agricultural or construction equipment. The use 

restrictions also have the effect of making use of the compound other 

than by manufacturers of automobiles and light-duty trucks or by 

 

6 HFC-134a, which is not an ozone depleting substance, has already 

largely replaced CFC-12 in motor vehicle air conditioners.
Page 20 of 32

commercial automotive service centers either illegal or highly 

unlikely.7

In the SNAP review, the EPA found that the use of HFO-1234yf in 

new passenger vehicle and light-duty truck MVAC systems, subject to 

the use conditions, does not present a significantly greater risk to 

human health and the environment compared to the currently approved

MVAC alternatives. In summary, the EPA’s SNAP review reached the 

following conclusions in support of this finding.

 Substituting HFO-1234yf for HFC-134a is environmentally 

beneficial from a climate change perspective as the global 

warming potential of HFO-1234yf is much lower (100 year GWP 

of 4 for HFO-1234yf vs. 100 year GWP of 1430 for HFC-134a). 

The EPA received a petition on May 7, 2010, (with a follow 

up petition on November 16, 2010) from the Natural 

Resources Defense Council, the Institute for Governance & 

Sustainable Development, and the Environmental 

Investigation Agency (a non-governmental organization) 

asking the EPA to remove HFC-134a from the list of 

acceptable substitutes under the SNAP program for use in 

motor vehicle air conditioners. The petitioners cited this 

 

7 While use by vehicle owners is not illegal, the SNAP conditions 

prevent the sale of HFO-1234yf in containers of the size that would 

be attractive to individual vehicle owners, and also include 

requirements for special connecting equipment for the large 

containers that are legal for sale. In addition, as described later 

in this notice, under a recent Significant New Use Rule anyone 

planning to distribute HFO-1234yf for use by a consumer would be 

required to notify the EPA before doing so.
Page 21 of 32

difference in GWP as a reason for the EPA to approve their 

request. 

 The use conditions of the final SNAP approval for HFO1234yf provide protection against potential safety hazards

related to the flammability of the compound, including 

potential exposure to hydrogen fluoride arising from 

thermal decomposition during a fire.

 Like HFC-134a, HFO-1234yf is not an ODS, so the 

substitution of the latter for the former will not affect 

stratospheric ozone concentrations.

 HFO-1234yf will not create significant impacts on ground 

level ozone or on local air quality.8

 The production of triflouroacetic acid from the atmospheric 

degradation of HFO-1234yf does not pose a significant risk 

of aquatic toxicity or ecosystem impacts.

 When used in accordance with the SNAP use restrictions, 

HFO-1234yf does not result in significantly greater risks 

to human health than the use of other available or 

potentially available substitutes.

The EPA conclusion in the final SNAP action regarding human 

health risks of HFO-1234yf was based on an extensive risk assessment 

 

8 In support of this conclusion, the final SNAP rule preamble cited 

two air quality modeling studies in addition to Luecken et al. These 

studies focused on air quality in Los Angeles, as a worst case 

scenario.
Page 22 of 32

and review of public comments. The EPA also noted that under the 

TSCA, the EPA had recently performed a pre-manufacture review for 

HFO-1234yf and adopted the SNUR (75 FR 65987, Oct. 27, 2010). The 

SNUR for HFO-1234yf requires reporting of additional information to 

the EPA before sale may begin for uses beyond air conditioning in new 

automobiles or commercial servicing of new automobiles built using 

HFO-1234yf, i.e., the EPA must be given 90-days notice before HFO1234yf products can be sold directly to consumers for the purpose of 

servicing, maintenance, and disposal. During these 90 days, the EPA 

can take further action to stop that marketing. This precautionary 

step was taken because of certain animal data indicating toxicity, 

and the possibility that home mechanics might accidentally expose 

themselves. Auto plant workers and repair shop professionals were 

expected to avoid exposure through work practices.9

Under the SNUR, the agency will: a) receive a Significant New 

Use Notice, or SNUN, of any person's intent to manufacture, import, 

or process HFO-1234yf for sale directly to consumers; b) have an 

opportunity to review and evaluate data submitted with the SNUN; and 

 

9

The EPA considered the results of developmental testing available at 

the time of the final SNUR action to be of some concern, but not a 

sufficient basis to find HFO-1234yf unacceptable under the SNUR 

determination. As a result, The EPA requested additional toxicity 

testing and issued the SNUR for HFO-1234yf. The EPA has received and 

is presently reviewing the results of the additional toxicity 

testing. The EPA continues to believe that HFO-1234yf, when used in 

new automobile air conditioning systems in accordance with the use 

conditions under the SNAP rule, does not result in significantly 

greater risks to human health than the use of other available 

substitutes.
Page 23 of 32

c) be able to regulate HFO-1234yf consumer products, if warranted. 

Any other potential applications beyond air conditioning in new 

automobiles or commercial servicing of new automobiles built using 

HFO-1234yf that may lead to significant exposures will also trigger 

the requirement for a SNUN, and would likely trigger further review 

under SNAP. The EPA believes these processes will provide adequate

opportunity to address any health effects issues associated with 

possible increased use of HFO-1234yf. 

The EPA’s SNAP program has also issued determinations of 

acceptability for HFO-1234ze as an acceptable substitute for certain 

ODS in a number of foam blowing end uses, as a refrigerant in nonmechanical heat transfer, and as a propellant as stated in Section I.

In this action, the EPA noted that HFO-1234ze is not ozone depleting, 

the GWP for HFO-1234ze is significantly lower than the GWPs for the 

ozone-depleting substances it will replace, HFO-1234ze is not 

flammable, and the toxicity risks of HFO-1234ze are low. For these 

reasons, the EPA found that HFO-1234ze will not pose a greater 

overall risk to human health and the environment than the other 

substitutes acceptable in these end uses. 

C. Conclusions

In summary, for both HFO-1234yf and HFO-1234ze, the EPA believes 

that (a) these chemicals qualify as negligibly reactive with respect 

to their contribution to tropospheric ozone formation, and (b) any 

non-tropospheric ozone related risks associated with potential 
Page 24 of 32

increased use are adequately addressed by other existing programs and 

policies. We also believe that the much lower global warming 

potential of HFO-1234yf compared to the compound HFC-134a for which 

it will substitute, as described in Section III.B, is an additional 

reason to approve the HFO-1234yf petition in particular, given that 

applying the Interim Guidance itself supports such approval. We 

invite the public to submit comments and additional information 

relevant to the issue of these compounds’ overall risks and benefits 

to human health and the environment, and on whether such information 

should be considered in connection with the decision to grant an 

exemption from the regulatory definition of VOC. 

IV. Proposed Action

The EPA is responding to the petitions by proposing to revise 

its definition of VOC at 40 CFR 51.100(s) to add HFO-1234yf and HFO1234ze to the list of compounds that are exempt from the regulatory 

definition of VOC because they are negligibly reactive on the basis 

that they are less reactive than ethane on a mass MIR basis. If an 

entity uses or produces any of these two compounds and is subject to 

the EPA regulations limiting the use of VOC in a product, limiting 

the VOC emissions from a facility, or otherwise controlling the use 

of VOC for purposes related to attaining the ozone NAAQS, then these 

two compounds will not be counted as a VOC in determining whether 

these regulatory obligations have been met. This action may also 

affect whether any of these two compounds are considered as VOCs for 
Page 25 of 32

state regulatory purposes to reduce ozone formation, if a state 

relies on the EPA’s definition of VOC. States are not obligated to 

exclude from control as a VOC those compounds that the EPA has found 

to be negligibly reactive. However, if this action is made final, 

states may not take credit for controlling these compounds in their 

ozone control strategies. 

V. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review and 

Executive Order 13563: Improving Regulation and Regulatory Review

Under Executive Order (EO) 12866 (58 FR 51735, October 4, 1993), 

this action is treated as a significant regulatory action because 

some may view it as raising novel legal or policy issues arising out 

of legal mandates. Accordingly, the EPA submitted this action to the 

Office of Management and Budget (OMB) for review under EO 12866 and 

13563 (76 FR 3821, January 21, 2011) and any changes made in response 

to OMB recommendations have been documented in the docket for this 

action.

B. Paperwork Reduction Act

This action does not impose an information collection burden 

under the provisions of the Paperwork Reduction Act, 44 U.S.C. 3501 

et seq. Burden is defined at 5 CFR 1320.3(b). It does not contain any 

recordkeeping or reporting requirement.

C. Regulatory Flexibility Act

The Regulatory Flexibility Act (RFA) generally requires an 
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agency to prepare a regulatory flexibility analysis of any rule 

subject to notice and comment rulemaking requirements under the 

Administrative Procedure Act or any other statute unless the agency 

certifies that the proposed rule will not have a significant economic 

impact on a substantial number of small entities. Small entities 

include small businesses, small organizations, and small governmental 

jurisdictions. For purposes of assessing the impacts of this notice 

on small entities, small entity is defined as: (1) A small business 

that is a small industrial entity as defined in the U.S. Small 

Business Administration (SBA) size standards. (See 13 CFR 121.); (2) 

A governmental jurisdiction that is a government of a city, county, 

town, school district or special district with a population of less 

than 50,000; and (3) A small organization that is any not-for-profit 

enterprise which is independently owned and operated and is not 

dominant in its field.

After considering the economic impacts of this proposed rule on

small entities, I certify that this action will not have a 

significant economic impact on a substantial number of small 

entities. This proposed rule will not impose any requirements on 

small entities. 

We continue to be interested in the potential impacts of the 

proposed rule on small entities and welcome comments on issues 

related to such impacts.

D. Unfunded Mandates Reform Act
Page 27 of 32

This action contains no federal mandates under the provisions of 

Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), 2 U.S.C. 

1531-1538 for state, local, or tribal governments or the private 

sector. The action imposes no enforceable duty on any state, local or 

tribal governments, or the private sector. Therefore, this action is 

not subject to the requirements of sections 202 and 205 of the UMRA. 

This action is also not subject to the requirements of section 

203 of UMRA because it contains no regulatory requirements that might 

significantly or uniquely affect small governments. 

E. Executive Order 13132 - Federalism

This action does not have federalism implications. It will not 

have substantial direct effects on the states, on the relationship 

between the national government and the states, or on the 

distribution of power and responsibilities among the various levels 

of government, as specified in Executive Order 13132. This action 

addresses the exemption of a set of chemical compounds from the VOC 

definition. Thus, Executive Order 13132 does not apply to this rule. 

In the spirit of Executive Order 13132, and consistent with the EPA 

policy to promote communications between the EPA and state and local 

governments, the EPA specifically solicits comment on this proposed 

rule from state and local officials.

F. Executive Order 13175: Consultation and Coordination with Indian 

Tribal Governments
Page 28 of 32

This action does not have tribal implications, as specified in 

Executive Order 13175 (65 FR 67249, November 9, 2000). It will not 

have substantial direct effects on tribal governments, on the 

relationship between the federal government and Indian Tribes, or on 

the distribution of power and responsibilities between the federal 

government and Indian Tribes, as specified in Executive Order 13175. 

Thus, Executive Order 13175 does not apply to this rule. 

Although Executive Order 13175 does not apply to this proposed 

rule, the EPA specifically solicits additional comment on this 

proposed rule from tribal officials.

G. Executive Order 13045: Protection of Children from Environmental 

Health and Safety Risks

This action is not subject to EO 13045 (62 FR 19885, April 23, 

1997) because it is not economically significant as defined in EO 

12866. While this proposed rule is not subject to the Executive 

Order, the EPA has reason to believe that ozone has a 

disproportionate effect on active children who play outdoors (62 FR 

38856; 38859, July 18, 1997). The EPA has not identified any specific 

studies on whether or to what extent these chemical compounds may 

affect children's health. The EPA has placed the available data 

regarding the health effects of HFO-1234yf in Docket No. EPA-HQ-OAR2003-0032 which is the docket for the SNUR for this compound.

The public is invited to submit comments or identify peerreviewed studies and data, of which the EPA may not be aware, that 
Page 29 of 32

assess results of early life exposure to the chemical compounds 

herein.

H. Executive Order 13211: Actions that Significantly Affect Energy 

Supply, Distribution, or Use

This action is not a “significant energy action” as defined in 

Executive Order 13211, “Actions Concerning Regulations That 

Significantly Affect Energy Supply, Distribution, or Use” (66 FR 

28355, May 22, 2001) because it is not likely to have a significant 

adverse effect on the supply, distribution, or use of energy. This 

action proposes to revise the EPA's definition of VOCs for purposes 

of preparing SIPs to attain the NAAQS for ozone under title I of the 

CAA.

I. National Technology Transfer and Advancement Act

Section 12(d) of the National Technology Transfer and 

Advancement Act of 1995 ("NTTAA"), Public Law 104-113, section 12(d), 

(15 U.S.C. 272 note) directs the EPA to use voluntary consensus 

standards in its regulatory activities unless to do so would be 

inconsistent with applicable law or otherwise impractical. Voluntary 

consensus standards are technical standards (e.g., materials 

specifications, test methods, sampling procedures, and business 

practices) that are developed or adopted by voluntary consensus 

standards bodies. The NTTAA directs the EPA to provide Congress, 

through OMB, explanations when the agency decides not to use 

available and applicable voluntary consensus standards. This 
Page 30 of 32

rulemaking does not involve technical standards. Therefore, the EPA 

is not considering the use of any voluntary consensus standards.

J. Executive Order 12898: Federal Actions to Address Environmental 

Justice in Minority Populations and Low-Income Populations

Executive Order (EO) 12898 (59 FR 7629, Feb. 16, 1994)

establishes Federal executive policy on environmental justice. Its 

main provision directs federal agencies, to the greatest extent 

practicable and permitted by law, to make environmental justice part 

of their mission by identifying and addressing, as appropriate, 

disproportionately high and adverse human health or environmental 

effects of their programs, policies, and activities on minority 

populations and low-income populations in the United States. 

The EPA has determined that this proposed rule will not have 

disproportionately high and adverse human health or environmental 

effects on minority or low-income populations because it will not 

affect the level of protection provided to human health or the 

environment.
Page 31 of 32

Page 31 of 32 - Air Quality: Revision to Definition of Volatile 

Organic Compounds – Exclusion of trans-1,3,3,3-tetrafluoropropene and 

2,3,3,3-tetrafluoropropene

List of Subjects in 40 CFR Part 51

Environmental protection, Administrative practice and procedure, 

Air pollution control, Ozone, Reporting and recordkeeping 

requirements, Volatile organic compounds.

_________________________

Dated: 

_________________________

Lisa P. Jackson,

Administrator.
*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote or Release During Review ***

EO12866_VOC Exemption_HFO_2060-AQ38_NPRM_FRN_20110906

Page 32 of 32

For reasons set forth in the preamble, part 51 of chapter I of 

title 40 of the Code of Federal Regulations is proposed to be 

amended as follows:

PART 51-REQUIREMENTS FOR PREPARATION, ADOPTION, AND SUBMITTAL OF 

IMPLEMENTATION PLANS.

 1. The authority citation for Part 51, Subpart F, continues 

to read as follows:

 Authority: 42 U.S.C. 7401, 7411, 7412, 7413, 7414, 7470-7479, 

7501-7508, 7601, and 7602.

§51.100 – [Amended]

 2. Section 51.100 is amended at the end of paragraph (s)(1) 

introductory text by removing the words “and perfluorocarbon 

compounds which fall into these classes:” and adding in their 

place a semi-colon and the words “; trans-1,3,3,3-

tetrafluoropropene; 2,3,3,3-tetrafluoropropene and 

perfluorocarbon compounds which fall into these classes:”.