[Federal Register Volume 60, Number 194 (Friday, October 6, 1995)]
[Proposed Rules]
[Pages 52357-52359]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-24938]



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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 82

[FRL-5313-1]


Protection of Stratospheric Ozone: Listing of Global Warming 
Potential for Ozone-Depleting Substances

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notice of proposed listing.

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SUMMARY: With this proposed action, the Environmental Protection Agency 
(EPA or the Agency) lists the global warming potentials for ozone-
depleting substances that are included as class I and class II 
controlled substances, or have been added as class I or class II 
controlled substances, under authority of section 602(e) of the Clean 
Air Act Amendments of 1990 (CAA). Class I and class II controlled 
substances are more fully described in a final rule previously 
published in the Federal Register on May 10, 1995. To meet EPA's 
statutory obligation under the CAA, this proposed listing cites the 
global warming potentials contained in the document, Scientific 
Assessment of Ozone Depletion: 1994, published by the United Nations 
Environment Programme (UNEP) in early 1995. As stated in the CAA, the 
listing of global warming potentials for class I and class II 
controlled substances ``shall not be construed to be the basis of any 
additional regulation under this Act.''

DATES: Written comments on this proposed listing must be received on or 
before November 6, 1995. Inquiries regarding public comments should be 
directed to the Stratospheric Ozone Information Hotline at 1-800-296-
1996.

ADDRESSES: Comments on this proposed listing should be submitted in 
duplicate (two copies) to: Air Docket No. A-92-13, U.S. Environmental 
Protection Agency, 401 M Street, SW., Room M-1500, Washington, DC 
20460.
    Materials relevant to this proposed listing are contained in Docket 
No. A-92-13. The Docket is located in room M-1500, First Floor, 
Waterside Mall at the address above. The materials may be inspected 
from 8 a.m. until 5:30 p.m. Monday through Friday. A reasonable fee may 
be charged by EPA for copying the docket.

FOR FURTHER INFORMATION CONTACT: Tom Land, Program Implementation 
Branch, Stratospheric Protection Division, Office of Atmospheric 
Programs, Office of Air and Radiation (6205J), 401 M Street, SW., 
Washington, DC 20460, (202) 233-9185. The Stratospheric Ozone Hotline 
at 1-800-296-1996 can also be contacted for further information.

SUPPLEMENTARY INFORMATION:

I. Background

    The temperature of the earth is determined by a balance between 
incoming energy from the sun and outgoing energy radiated from the 
earth's surface and atmosphere. Ultraviolet and visible radiation from 
the sun pass through the earth's atmosphere and strike the earth's 
surface. The earth radiates this energy from the sun back into the 
atmosphere in the form of infrared radiation in a process called 
radiative forcing. Certain constituents of the atmosphere, such as 
carbon dioxide and water vapor, absorb the infrared radiation and trap 
it in the atmosphere in a process known as the greenhouse effect. The 
trapped infrared radiation warms the earth's surface and the 
troposphere (lower atmosphere). The warming of the earth's surface and 
the troposphere through the balance between absorbed energy and 
radiated energy determines the climate of the planet.
    The molecular structure of a chemical determines its ability to 
absorb infrared radiation in the atmosphere. Scientists use an index 
called the global warming potential (GWP) to quantify the relative 
capability of different chemicals to absorb radiated infrared 
radiation. Three factors contribute to a chemical's relative 
contribution to this radiative forcing process. The three factors are 
the primary input in the formulation, calculation and use of the 
radiative forcing index known as the GWP. The three factors that 
contribute to the relative radiative forcing potential of a chemical 
are: (1) The capacity to absorb the different wavelengths of infrared 
energy, (2) the residence time in the atmosphere, and (3) the time 
period over which the radiative effects will be considered. The first 
two of these factors are technical, and the third is dependent on the 
interests of the user. In addition to these direct radiative effects, 
some chemicals, such as ozone-depleting substances, have an indirect 
effect on radiative forcing due to interactive atmospheric processes.
    Molecules containing carbon-chlorine bonds and carbon-fluorine 
bonds, such as the ozone-depleting substances controlled under the 
Montreal Protocol and Title VI of the Clean Air Act Amendments of 1990, 
absorb radiation emitted by the earth that would otherwise escape into 
space. In defining the relative capability of ozone-depleting 
substances to affect radiative forcing, scientists assign a GWP to a 
specific substance, such as dichlorodifluoromethane (CFC-12). Research 
to define the GWP for each of 

[[Page 52358]]
the class I and class II ozone-depleting substances, as well as other 
substances, is being conducted by scientists throughout the world. The 
potential of chlorofluorocarbons (CFCs) to provide significant 
radiative warming to the troposphere has been understood for more than 
15 years. However, the exact radiative forcing effect of CFCs and other 
ozone-depleting substances relative to other chemicals is still being 
investigated. Scientists are still researching the interaction between 
atmospheric processes, seasonality, long-term changes in climate, the 
introduction of chemicals produced by humans into the atmosphere and 
the uncertainties inherent in the interaction of these complex 
processes.

II. Referencing Recently Published Scientific Documents

    EPA believes that three recently published scientific documents 
represent the most up-to-date international scientific knowledge 
regarding GWPs for class I and class II controlled substances. EPA 
referencing these three scientific documents and the list of GWPs they 
contain in order to meet the Agency's statutory obligations under 
Section 602(e) of the CAA to publish GWPs for class I and class II 
controlled substances. These documents are also referenced in part, for 
their discussions of different radiative forcing indices and the 
indirect effects of ozone-depleting substances on radiative forcing. 
These documents demonstrate the current state of knowledge and the 
current uncertainties involved in calculating the GWPs for class I and 
class II controlled substances.
    The citation for the three scientific documents that report on GWPs 
for class I and class II controlled substances are:

    United Nations Environment Programme (UNEP), February 1995, 
Scientific Assessment of Ozone Depletion: 1994, Chapter 13: ``Ozone 
Depleting Potentials, Global Warming Potentials and Future Chlorine/
Bromine Loading;''
    Intergovernmental Panel on Climate Change (IPCC), 1995, Climate 
Change 1994: Radiative Forcing of Climate Change and An Evaluation 
of the IPCC IS92 Emission Scenarios, ``Summary for Policymakers: 
Radiative Forcing of Climate Change,'' pages 32-34; and
    Daniel, John S., Susan Solomon and Daniel L. Albritton, January 
20, 1995, Journal of Geophysical Research, Vol. 100, No. D1, ``On 
the evaluation of halocarbon radiative forcing and global warming 
potentials.''
    Chapter 13 in the UNEP, Scientific Assessment and pages 32 
through 34 in the IPCC, Summary for Policymakers describe the 
factors considered in calculating various radiative forcing indices, 
such as (1) the direct GWP, (2) the absolute global warming 
potential (AGWP), and (3) the net GWP per unit mass emission. 
Chapter 13 of the Scientific Assessment and the article by John S. 
Daniel, et. al. in the Journal of Geophysical Research describe the 
indirect feedback effects of ozone-depleting substances on the 
temperature of the atmosphere, and therefore the potential indirect 
effects that depletion of stratospheric ozone has on the calculation 
of the GWP.

III. Listing GWPs for class I and class II Controlled Substances

    With today's action, EPA proposes publication of the GWPs that are 
listed for class I and class II controlled substances in the Scientific 
Assessment of Ozone Depletion: 1994 as published by the United Nations 
Environment Programme (UNEP) under the auspices of the Montreal 
Protocol in February of 1995. The GWPs for class I and class II 
controlled substances as published in the Scientific Assessment are in 
Appendix I to Subpart A--Global Warming Potentials.
    The Scientific Assessment of Ozone Depletion: 1994 does not list a 
GWP for every controlled substance that is listed in Appendices A and B 
to Subpart A as most recently promulgated in the Federal Register on 
May 10, 1995 (60 FR 24970). For some ozone-depleting chemicals, such as 
methyl bromide, scientists have not developed a full infrared spectrum 
that is necessary to calculate the relative radiative forcing potential 
of a substance. Each chemical absorbs the Earth-emitted infrared 
radiation in specific energy (or wavelength) bands determined by the 
quantum-mechanical properties of the specific molecule.1 
Scientists have not measured the spectral region in which some of the 
ozone-depleting substances absorb infrared radiation. In addition, more 
data must be collected on the tropospheric distribution and 
concentration of some of the chemicals, their atmospheric lifetimes, 
and the interactive atmospheric chemistry in order to complete a 
calculation of the global warming potential for the remaining ozone-
depleting substances. Scientific centers and academic institutions 
throughout the world are undertaking the necessary measurements and 
studies that are needed to complete the calculations of GWPs for other 
ozone-depleting substances. EPA believes it is not possible at this 
time to publish GWPs for every ozone-depleting substance listed in 
Appendix A and B to Subpart A because the necessary scientific 
information is not available. EPA will continue to evaluate GWPs for 
class I and class II controlled substances not listed in today's 
proposal and as deemed appropriate amend the listing through rule 
making.

    \1\ Wuebbles, Donald J., 1995, ``Weighing Functions for Ozone 
Depletion and Greenhouse Gas Effects on Climate,'' Annual Review of 
Energy and Environment, 20:45-70.
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List of Subjects in 40 CFR Part 82

    Environmental protection, Administrative practice and procedure, 
Air pollution control, Chemicals, Chlorofluorocarbons, Exports, 
Hydrochlorofluorocarbons, Imports, Ozone layer, Reporting and 
recordkeeping requirements, Stratospheric ozone layer.

    Dated: September 29, 1995.
Carol Browner,
Administrator.
    40 CFR part 82 is proposed to be amended as follows:

PART 82--PROTECTION OF STRATOSPHERIC OZONE

    1. The authority citation for part 82 continues to read as follows:

    Authority: 42 U.S.C. 7414, 7601, 7671-7671q.

    2. Appendix I is added to Subpart A to read as follows:

 Appendix I to Subpart A--Global Warming Potentials (Mass Basis), Referenced to the Absolute GWP for the Adopted
 Carbon Cycle Model CO2 Decay Response and Future CO2 Atmospheric Concentrations Held Constant at Current Levels
                                      [Only direct effects are considered]                                      
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                                                                               Global warming potential (time   
                                                                                          horizon)              
                 Species (chemical)                    Chemical formula   --------------------------------------
                                                                             20 years    100 years    500 years 
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CFC-11.............................................  CFCl3                        5000         4000         1400

[[Page 52359]]
                                                                                                                
CFC-12.............................................  CF2Cl2                       7900         8500         4200
CFC-13.............................................  CClF3                        8100        11700        13600
CFC-113............................................  C2F3Cl3                      5000         5000         2300
CFC-114............................................  C2F4Cl2                      6900         9300         8300
CFC-115............................................  C2F5Cl                       6200         9300        13000
H-1301.............................................  CF3Br                        6200         5600         2200
Carbon Tet.........................................  CCl3                         2000         1400          500
Methyl Chl.........................................  CH3CCl3                       360          110           35
HCFC-22............................................  CF2HCl                       4300         1700          520
HCFC-141b..........................................  C2FH3Cl2                     1800          630          200
HCFC-142b..........................................  C2F2H3Cl                     4200         2000          630
HCFC-123...........................................  C2F3HCl2                      300           93           29
HCFC-124...........................................  C2F4HCl                      1500          480          150
HCFC-225ca.........................................  C3F5HCl2                      550          170           52
HCFC-225cb.........................................  C3F5HCl2                     1700          530          170
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United Nations Environment Programme (UNEP), February 1995, Scientific Assessment of Ozone Depletion: 1994,     
  Chapter 13, ``Ozone Depleting Potentials, Global Warming Potentials and Future Chlorine/Bromine Loading.''    


[FR Doc. 95-24938 Filed 10-5-95; 8:45 am]
BILLING CODE 6560-50-P