[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
