United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S8-90/079 Jan. 1991
EPA Project Summary
Evaluation of Significant
Anthropogenic Sources of
Radiatively Important Trace
Gases
S. D. Piccot, A. Chadha, J. DeWaters, T. Lynch, P. Marsosudiro, W. Tax,
S. Walata, and J. D. Winkler
Emissions of greenhouse gases from
human activities, Including fossil fuel
combustion, Industrial/agricultural ac-
tivities, and transportation, contribute
to the Increasing concentrations of
radlatively Important trace gases
(RITGs) in Earth's atmosphere. In order
to evaluate the extent to which these
anthropogenic (human) activities will
influence future atmospheric composi-
tion and climate, it is necessary to
identify all significant global sources
and sinks, and to characterize the
strengths of these sources. Trace gases
of concern include carbon dioxide
(CO), nitrous oxide (N2O), methane
(CHj, chlorofluorocarbons (CFCs) and
ozone (O,). Several gases which are not
themselves radlatively active, but which
can contribute to the buildup of a
radiatively active trace gas, include
oxides of nitrogen (NO) and
nonmethane hydrocarbons (NMHCs).
These compounds play a key role In
the formation of ozone in the tropo-
sphere.
The U.S. EPA has conducted several
emissions research projects to evaluate
and better characterize emissions from
specific sources of RITGs. The purpose
of these emissions research projects
was to rank sources of RITGs In terms
of their potential impacts on radiative
forcing and to develop country- and
source-specific emission factors where
data were adequate to warrant emission
factor development. In addition, for
some source categories, preliminary
country-specific Information was col-
lected which could be of use in future
emission factor research. One of the
objectives of this document is to inte-
grate the results of these research
projects and to identify areas where
further research Is needed.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Tri-
angle Park, NC, to announce key find-
Ings of the research project that Is fully
documented In a separate report of the
same title (see Project Report ordering
Information at back).
Approach
The methodology used in this study in-
volved two levels of screening: a prelimi-
nary source assessment, followed by a
detailed source characterization. The pre-
liminary source assessment evaluated a
source's contribution to estimated global
radiative forcing, evaluated the potential
for emissions from that source to vary
from country to country, and assessed
potential data weaknesses. Based on the
results of the preliminary source assess-
ment, the detailed source characterization
involved development of improved emis-
sions data, and where data were adequate,
country-specific emission factors.
Table 1 identifies RITG sources that
were assessed and those chosen for fur-
ther evaluation by source characteriza-
tion. In some cases, available country-
specific data were inadequate to support
emission factor development. In these
cases, data availability as well as data
needs were documented. As follow-on re-
search to this study, several sources were
GyQ Printed on Recycled Paper
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Tab/0 1. Summary of Source-Specific Studies Conducted
Source
County-Specific
Associated Preliminary Emission Factor Further
Gases Assessment Development' Research*
Utility Coal-fired
Boilersc
Utility Oii/Gas-fired
Boilers
Industrial Boilersc
Coal Mines
Natural Gas Transmission/
Distribution
Transportation
Rice Cultivation
Crop Fertilization
Municipal Solid Waste
Landfills
Deforestation
Misc./tndustrial/Other
Sources"
Res/lnd CFC Use
Residential Wood
Combustion
Residential/Commercial
Fossil Fuel
CO, NO,
CO, NO,
CO, NO,
CHf
CH4
NO, VOC, CO,
COPN,O
CH4
A/,0
CH4
CO, CH,
CH4
CFC
CO, NO,
CO, NO,
x
X
X
X
X
X
X
X
X
X
X
X
' Detailed assessments were conducted for some sources with the initial intent of developing
country-specific emission factors. However, emission factors could not be developed for all
sources because of limitations in readily available data.
* Note: Sources evaluated in the Further Research stage are not within the scope of this project.
c Country-specific data developed for utility coal-fired boilers are also applicable to industrial coal-
fired boilers.
* These sources include transportation, solvent use, coke production, chemical manufacturing and
all other sources included in a global VOC inventory model developed by EPA.
chosen for a third stage of research in
other projects. These are identified in Table
1. A more detailed discussion of these
evaluations follows.
Preliminary Source
Assessments
Overview of Assessments
Preliminary source assessments were
conducted as a first step in the process of
developing improved emissions estimates.
The objectives of the preliminary source
assessments were to (1) assemble and
evaluate current global emissions esti-
mates, determine the weaknesses in those
estimates, and identify sources whose
emissions characteristics are most uncer-
tain on global scales and are thus in need
of improvement; (2) estimate and evalu-
ate the significance of the contribution of
individual sources of RITGs to global
emissions and potential global warming;
and (3) assess the potential for emissions
from key sources to vary from country to
country based on technological or other
differences which may exist between
countries.
A major objective of this project was to
develop a relative ranking of the signifi-
cance of major sources of RITGs, or
greenhouse gases. The first step was to
develop a set of greenhouse gas signifi-
cance (GGS) factors for CO2. CH4, N2O,
CFCs, and NO, emitted by anthropogenic
sources; these factors equal the percent-
age of total estimated global warming, oi
total 'radiative forcing potential* (RFP), at
tributabte to these emissions between 198J
and 1990 (the period selected for this
analysis). Once these factors were devel
oped, they were multiplied by the fractior
of total global emissions of each gas at
tributable to a specific sourcethe globe
emissions significance (GES) factor. Thi
result of this second step was the RFP c
a specific gas from a specific source, o
the percentage of total estimated globs
warming attributable to emissions of the
gas from that source. The gas-specif*
RFPs for each source were then summe<
to obtain the total RFP for each majc
source of RITGs.
Between 1985 and 1990, the estimate-
percentage contributions to potential gtotx
warming, or GGS factors, or the RITG
evaluated in this study are: CCL 54; CH
20; NO, 8; and tropospheric 63, 7. DC
tails of the development of these factoi
and their use in determining the total RFP
for each major source of RITGs are ore
vided in the full report. The assessment <
results from that effort are given below.
Results of Assessments
The most significant source of RIT
emissions is industrial and utility coal us
(this group includes coal combustion an
coal mining), which is estimated to have
total RFP of 17; i.e., 17% of total glob
radiative forcing. Emissions of CO accou
for over 14% of the estimated forcin
while CH and NO emissions account f
about 3%. If residential and commerci
coal use is also considered, the radiath
forcing associated with the global uses
coal (burning and mining) is estimated
be about 20%.
Several other source categories co
tribute significantly to radiative forcing (si
Table 2). These categories include ag
cultural activities (e.g., CH4 emissions frc
rice cultivation, and N2O emissions frc
general tilling and fertilizing), industrial a
residential CFC use, and CO2 and N
from transportation sector oil consumptk
Each is estimated to have a total RFP
11. Deforestation from forest burning ;
tivities contributes significant quantities
CO, and is estimated to have a total R
of 9. The loss of forests results in the k
of a sink for CO2 emissions which is
negative feedback not included in the f;
tors above.
Industrial and residential CFC use
estimated to have a total RFP of
Transportation sector fuel consumpt
contributes significant emissions of C
and NO,. In addition, the transportat
sector is one of the most potentially !
nificant sources contributing to troposphi
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Table 2. Estimated Total Radiative Forcing Potential Associated with Major Source Groups
General
Source Group
Description
Estimated
Contribution to Radiative
Forcing (%)
Key
Greenhouse Gases
Primary
Secondary
Utility and Industrial
Coal Use (includes mining)
Rice Cultivation and
General Tilling and
Fertilizing
Industrial and Residential
CFC Use (includes automobile
air conditioning units)
Transportation Sector Oil
Consumption
Deforestation
Residential Wood Combustion
Residential and Commercial
Fossil Fuel Combustion
(coal, oil, gas)
Industrial Oil Combustion
Utility and Industrial Gas
Consumption, Industrial
Process Emissions,
Cement Manufacturing,
Waste Disposal Sources,
Fuel Production, and Ruminants
Total
17
11
11
11
9-
9"
7
6
19
CO,
CH,, NO,
N,O
CFCs
CO.
CO.
CO.
CO,
CO.
CO, NO.
NO.
CHf A/,0
N,0
CH4
NO.
100
'The total forcing associated with deforestation is actually about 20%. However, the CO NfO, and
CH4 emissions and the loss of CO, sink activity are split between the agricultural and residential
sectors since an estimated 50% of the wood cut in deforestation is burned for residential heating
and cooking. This analysis does not take into account that the combustion processes between field
and residential appliance combustion may differ and .thus, the emissions may also differ.
ozone because of the high NO,, VOC and
CO emissions associated with automobile
use in urban areas. Table 2 shows that
several other fuel combustion groups
contribute significantly to radiative forcing.
These include residential wood combus-
tion, estimated to have a total RFP of 9;
residential and commercial fossil fuel use,
estimated to have a total RFP of 7; and
industrial oil combustion, estimated to have
a total RFP of 6. As with utility and indus-
trial coal use, CO2 emissions account for
most of this forcing, while NO,, N2O, and
CK are estimated to contribute the rest.
The analysis to rank source categories
of greenhouse gases by their radiative
'forcing potential was not the only factor
considered in choosing the sources to be
evaluated in greater detail. Since one ob-
jective of this research was to devebp
country-specific emission factors where
possible, a preliminary evaluation was
conducted to identify sources which have
a potential to vary significantly from coun-
try to country. Each of the sources evalu-
ated was assessed for this variation po-
tential. Oil combustion in industrial and
utility boilers is a source of greenhouse
gases, but these emissions do not vary
significantly from country to country be-
cause fuel quality and combustion effi-
ciency are relatively consistent. However,
transportation sector fuel consumption is
a major source of NO, emissions, and
these emissions vary significantly from
country to country due to differences in
fuel efficiency and applied emissions con-
trols. CH4 emissions from rice cultivation
vary due to differences in climate, number
and length of growing season(s), and the
average soil temperature of the rice
growing region. CH4 emissions from mu-
nicipal solid waste (MSW) landfills vary
according to waste composition, waste
disposal method, climate, and design
characteristics of the landfill. Natural gas
transmission and distribution systems emit
CH, as a function of throughput, system
design and maintenance, and pipeline
construction materials.
A great deal of uncertainty surrounds
existing emissions estimates for many
source types. One objective of EPA's glo-
bal climate research is to identify areas
where uncertainty can be reduced. In
general, emissions estimates for most CH
sources are the least certain; because of
this, significant emphasis was placed on
evaluating several key CH4 sources in
more detail. EPA is currently conducting
measurements research programs to im-
prove the understanding of coal mine CH
emissions as well as emissions from MSW
landfills and natural gas production and
distribution facilities.
Detailed Source
Characterizations
Overview of Characterizations
The objectives of the detailed source
characterizations were to develop im-
proved emissions data and, where data
were adequate, to devebp country-specific
emission factors for key sources. Another
objective was to identify the additional data
and analysis needed to make further im-
provements in the emission factors for
key sources. Under the source character-
izations, country-specific fuel, technology,
and other data were obtained in an effort
to develop more representative emission
factors for the key sources of RITGs
identified in the preliminary assessments.
Where adequate supporting data were
available, country-specific emission factors
were developed.
Results of Characterizations
Based on the results from the prelimi-
nary source assessments, country-specific
emission factors were developed for coal-
fired utility boilers, natural gas production/
distribution sources, transportation
sources, MSW landfills and rice cultivation.
Improved country-specific data were de-
veloped for coal mining operations, but
these data were insufficient for developing
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country-specific emission factors. Ongo-
ing research is being conducted by EPA
to support the development of coal mine
emission factors and improved global
emissions estimates from coal mine ven-
tilation (see discussion below). Brief de-
scriptions of the sources evaluated are
provided below, along with tables of
emission factors developed in this study.
Utility Coal-Fired Boilers
Coal combustion technologies are sig-
nificant sources of CO2 and to a lesser
extent, ozone precursors such as NO,, and
VOC. Based on calculations performed
for this study, coal-fired utility boilers are
estimated to account for approximately
10% of total global radiative forcing due to
emissions of CO2 and NO,. Factors which
can significantly affect emissions from
utility boilers include overall generating
station efficiency, the extent of electricity
use within the plant (partially driven by the
use of emissions controls), fuel quality
parameters such as coal heat content and
carbon content, electrical transmission
system and distribution system efficiency,
type of controls used (if any), and the
general boiler design. Because these fac-
tors can vary significantly from country to
country, country-specific information was
obtained for these factors so representative
emission factors could be developed. The
factors taken into account in developing
CO, emission factors for this study include
fuefquality (heat content and carbon con-
tent) and generation station efficiency
(busbar efficiency). Transmission line loss
data are also presented because these
data are needed for emissions modeling
and other RITG research. Emission factors
range from 44,620 g CO -C/GJ in Finland
to 159,003 g CO2-C/GJ in Pakistan (as a
point of reference, the U.S. is 74,767 g
CO2-C/GJ). The countries for which emis-
sion factors were developed account for
more than 99% of coal combustion in utility
boilers.
Some initial data on the types of NOX
controls used in some Organization for
Economic Cooperation and Development
(OECD) countries and the NO, emissions
standards used in several countries were
also identified. However, these data were
not sufficient to warrant the development
of country-specific NOX emission factors for
coal-fired boilers.
Natural Gas Production/
Distribution Systems
Natural gas consists of 89 to 93% CH4
and losses of natural gas through gas
production and distribution systems have
been estimated to account for 9 to 12% of
total annual global CH4 emissions from
anthropogenic sources. Factors which may
affect CH4 emissions from production and
distribution systems include the age and
condition of the system, the construction
materials, the total length of pipeline and
the number and type of fittings, the system
throughput, and perhaps climate and soil
conditions. Country-specific emission fac-
tors developed in this study range from
0.2% loss (percent of natural gas through-
put) in Tunisia to 5.5% in Argentina (as a
point of reference, the U.S. is 1.3%). The
countries evaluated for emission factor
development account for about 75 percent
of global natural gas production in 1985.
These factors can be multiplied by a
country's pipeline system throughput to
estimate CH4 emissions for each country.
For this study, throughput was defined as
the sum of indigenous production (minus
exports) plus any imports. These emission
factors attempt to account for gas lost to
the atmosphere after the first metering
point in the natural gas production and
distribution system. As a consequence,
they may not take into account gas tost at
the well head itself. EPA is currently con-
ducting research to characterize CH4
emissions from natural gas operations.
Municipal Solid Waste Landfills
Municipal solid waste landfills have been
estimated to account for between 4 and
15 percent of global CH4 emissions from
anthropogenic sources. Country-specific
parameters affecting emissions include per
capita waste generation rate, waste com-
position, fraction of waste landfilled, and
any CH4 recovery practices employed.
Emission factors developed for countries
where sufficient data were available to
support emission factor development take
into account the percent of waste landfilled,
percent degradable organic content, and
waste generation rates. Country-specific
data from 31 countries representing ap-
proximately 67% of the global population
were collected in developing these emis-
sion factors. The emission factors range
from 1.6 kg CH4/caprta/yr in Switzerland to
42 kg/capita/yr in Canada (as a point of
reference, the U.S. is 36 kg/capita/yr).
Transportation Sources
Motor vehicles emit many pollutants in-
cluding hydrocarbons, CO, NOK and CO2,
all of which contribute to global climate
change. Based on research conducted in
this study, transportation sector fuel con-
sumption is estimated to account for about
11% of the radiative forcing potential as-
sociated with anthropogenic sources.
Factors affecting emissions from motor
vehicles within a specific country include
fleet average fuel efficiency (a function of
automobile efficiency and fleet retireme
rate) and the level of emissions cent
achieved by each country (i.e., the degr
to which crankcase ventilation, exhai
controls, engine modifications, and tw
or three-way catalysts are applied). The
factors must be characterized to devel
country-specific emission factors. Count
specific CO2, CO, and NO, emission fi
tors developed for light duty gasofir
powered vehicles for 37 countries wh<
data were available represent 88% of 1
world vehicle fleet. The emission fact)
range: from 6752.7 g COJgal.* in mi
developing countries to 7977.6 g CO/g
in Japan (with 7892.6 in the U.S.); frt
39.2 g NOx/gal. in Japan to 55 g NO/gal
most developing countries (with 41.6
the U.S.); and from 339.8 g CO/gal.
Japan to 871 g CO/gal. in most develop
countries (with 378.2 in the U.S). Mi
general uncontrolled global emission f
tors for light duty diesel vehicles are e
mated to be 7675 g CO/gal., 23 g CO/g
and 24 g NO/gal. Given that assumptic
are made for future fuel efficiency i
control levels, the country-specific d
developed for transportation sources c
be used to estimate emission factors wh
are representative of the future fleet
automobiles.
Rice Cultivation
CH4 emissions from wet rice cuftival
are estimated to account for about 30°/
total global emissions of CH4. Given
approximate radiative forcing potentia
CH4, wet rice cultivation therefore is e
mated to account for about 6% of t<
global radiative forcing. The factors aff<
ing CH4 emissions from rice cultivation
elude the total land area under rice c
vation in a country, the number of grov
days per year (a function of the nurr
and length of the growing seasons),
the release rate of CH4 per hectare
year. The release rate is strongly correl;
with average soil temperature, whicl
turn is a function of the type of sea
(wet or dry). These factors were all <
sidered in developing country-spe
emission factors. The countries for w
emission factors were developed acci
for more than 90 percent of world
production. Except for emission fat
developed for tow temperatures (19-2C
the difference between the two set
emission factors is fairly consistent.
wet season emission factors develc
from Italian data tend to be about t
times higher than those developed
the Spanish data, while the dry se;
i gal. - 3.81.
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emission factors are about four times
higher. The wet season emission factors
range from 1.9 mg/m'/hr in Japan (Span-
ish data) to 41.7 mg/m2/hr in Bangladesh
(Italian data). The dry season emission
factors range from 1.8 mg/m2/hr in India
(Spanish data) to 28.3 mg/m2/hr in Indo-
nesia (Italian data)
A number of other factors affect CH4
emissions but insufficient data exist to in-
corporate these factors into current emis-
sion factor estimates. These factors include
the effects of fertilizer use, the presence
of salts in the paddy water, the effect of
the organic composition of the paddy soil,
and the effects of plant density on CH
emissions. These additional factors should
be explored if future research is conducted
to characterize CH4 emissions from rice
cultivation.
Coal Mining
CH4 emissions from coal mines are es-
timated to contribute approximately 10%
of total global CH4 emissions. The matu-
ration of a coal seam produces CH, by
biogenic and thermogenic processes. CH4
release from a coal mine depends on many
factors, including the amount and rank of
coal obtained from underground and sur-
face mines, the underground mining tech-
nique used, underground and surface mine
depth, coal rank and characteristics, coal-
bed CH4 content, gob gas quantities and
characteristics, and current CH4 recovery
and use practices. Improved country-spe-
cific data were developed for coal mining
operations, but these data were not com-
plete enough to warrant country-specific
emission factor development. Further re-
search was conducted by EPA to develop
emission factors based on relationships
between measureable physical parameters
related to coal mining. A global estimate
of CH emissions from the ventilation air
of coal mining operations was also devel-
oped in the course of this research. These
research results will be provided in a
forthcoming EPA report.
Industrial/Other Sources of CH4
Little attention has been given to smaller
anthropogenic sources of CH4 in past
studies characterizing anthropogenic CH4
emissions. The objectives of the prelimi-
nary assessment of industrial/other
sources of CH4 were to identify previously
uncharacterized anthropogenic sources of
CH4, to develop preliminary estimates of
the amount of CH4 released by these
sources, to evaluate the quality of the
data used to make these estimates, and
to determine any potential data weak-
nesses or additional data needs. CH4
emissions from numerous anthropogenic
source types were estimated using a glo-
bal emissions inventory model. These es-
timates were compared to other estimates
to identify globally significant source types.
Model input data were evaluated to assess
data quality. The five most significant
source groups identified in this assessment
were fuel-wood burning, coke production,
refuse disposal (not including MSW land-
fills), miscellaneous industrial other, and
rubber, plastic, and other organic chemical
manufacturing.
Principal Findings
Principal findings of the research dis-
cussed in this report are listed below:
The most significant group of sources is
utility and industrial coal use (including
mining), which contributes significant
quantities of CO2, CH,, and NO, to the
global atmosphere.
Rice cultivation and general tilling and
fertilizing, industrial and residential CFC
use, and transportation sector oil con-
sumption also contribute significantly to
total global warming.
Sources of CH, (including coal mining,
natural gas production/distribution sys-
tems, MSW landfills, rice cultivation, and
miscellaneous industrial sources) were
identified as general areas of uncertainty
needing evaluation.
As a result of the detailed source char-
acterizations, country-specific emission
factors were developed for coal-fired
utility boilers, natural gas production/
distribution systems, transportation
sources, municipal solid waste landfills,
and rice cultivation.
Future Data Needs
When research projects are conducted
on global scales, difficulties are encoun-
tered with the availability, reliability, and
consistency of varbus types of data. The
research conducted here to improve the
understanding of the country-specific
emissions characteristics of specific
sources is no exception. One objective of
these studies was to identify data gaps
and data needs; this section summarizes
those deficiencies for sources for which
detailed assessments were conducted and,
to a lesser extent, for some sources where
only preliminary assessments were con-
ducted. These data gaps and data needs
include:
Although CO2 emissions from utility and
industrial coal-fired boilers Have been
extensively researched, less information
is available about NO. Data needs in-
clude information on ooiler population
and design, combustion parameters, and
coal types.
There are many data gaps in the cur-
rent understanding of CH^ emission from
natural gas production/distribution sys-
tems. Most measurements at transfer
points are currently made at an accuracy
of about 1%. A methodology is needed
to accurately characterize CH4 losses
from natural gas production/distribution
systems besides the losses at transfer
points.
Future research on coal mining needs
to expand the focus of past research
efforts by (1) developing relationships
describing coal-bed CH4 content on the
basis of measureable physical param-
eters, (2) using the information devel-
oped in (1) to develop estimates of the
CH4 content of mine ventilation air (the
largest single source of CH4 from min-
ing operations), and (3) ultimately, ex-
trapolating this methodology to develop
global estimates of CH4 emissions from
coal mines. This further research will be
documented in a forthcoming EPA re-
port.
Factors affecting CH, emissions from
MSW landfills which need further char-
acterization include the effect of build-
ing landfills above ground rather than
below ground, the effects of moisture
and ambient temperature on CH4 pro-
duction, and the extent of the use of
gas collection systems. In addition, more
country-specific information on the fac-
tors which influence CH4 generation
(e.g., waste composition, per capita
waste generation rate, and prevalence
of landfills as a disposal method) is
needed.
Factors affecting CH4 emissions from
rice cultivation which need to be further
researched include the use of fertilizer,
the presence of salts in the paddy water,
plant density, and composition and
temperature of paddy soils. More coun-
try-specific information is generally
needed as well, particularly studies
which focus on rice cultivation in the
Far East.
In the area of transportation, country-
specific retirement rates, emissions
control data, import/export, and produc-
tion data are needed. The effect of fuel
efficiency on carbon-based species
needs to be quantified.
Key uncertainties are associated with
the raw data and the methods used to
interpret and use the data for develop-
ing the global CH inventory of miscel-
laneous sources of CK.
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An additional analysis conducted as part This analysis indicated a consensus emissions. This emphasizes the need f<
of this study examined atmospheric among atmospheric chemistry modelers better understanding of the global intera
chemistry research needs rather than that the most significant emissions re- tions of NO(, CH4, and other RITGs.
mitigation or control strategy scenarios. search need was better inventories of NO(
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S. Pkxot, A. Chadha, J. DeWaters, T. Lynch, P. Marsosudiro, W. Tax, S. Walata,
andJ. Winkterare with Alliance Technologies Corp., Chapel Hill, NC 27514.
Julian W. Jones is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Significant Anthropogenic Sources of
Radiativety Important Trace Gases," (Order No. PB 91-127 7S3/AS; Cost: $23.00,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati, OH 45268
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Penalty for Private Use $300
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