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The emissions calculated using Tier 2 should be reported following the IPCC Reporting
Instructions:• I A 3 a i International aviation (international bunkers) - note: as far
as possible, these emissions are to be excluded from national totals andreported separately.
• I A 3 a ii Domestic aviation
TABLE 1-50
EXAMPLES OF AIRCRAFT TYPES AND EMISSION FACTORS FOR LTO CYCLESAS WELL AS FUEL CONSUMPTION PER AIRCRAFT TYPE
Emission factors(kg/LTO)

Fuel
consumption(kg/LTO)

Aircraft type(a)CO2CH4 (b)N2O(c)NOXCO

NMVOC(b)SO2(d)

A300

5470

1.0

0.2

27.21

34.4

9.3

1.7

1730

A310

4900

0.4

0.2

22.7

19.6

3.4

1.5

1550

A320

2560

0.04

0.1

11.0

5.3

0.4

0.8

810

BAC1-11

2150

6.8

0.1

4.9

67.8

61.6

0.7

680

BAe 146

1800

0.16

0.1

4.2

11.2

1.2

0.6

570

B707*

5880

9.8

0.2

10.8

92.4

87.8

1.9

1860

B727

4455

0.3

0.1

12.6

9.1

3.0

1.4

1410

B727*

3980

0.7

0.1

9.2

24.5

6.3

1.3

1260

B737-200

2905

0.2

0.1

8.0

6.2

2.0

0.9

920

B737*

2750

0.5

0.1

6.7

16.0

4.0

0.9

870

B737-400

2625

0.08

0.1

8.2

12.2

0.6

0.8

830

B747-200

10680

3.6

0.3

53.2

91.0

32.0

3.4

3380

B747*

10145

4.8

0.3

49.2

115

43.6

3.2

3210

B747-400

10710

1.2

0.3

56.5

45.0

10.8

3.4

3390

B757

4110

0.1

0.1

21.6

10.6

0.8

1.3

1300

B767

5405

0.4

0.2

26.7

20.3

3.2

1.7

1710

Caravelle*

2655

0.5

0.1

3.2

16.3

4.1

0.8

840

DC8

5890

5.8

0.2

14.8

65.2

52.2

1.9

1860

DC9

2780

0.8

0.1

7.2

7.3

7.4

0.9

880

DC10

7460

2.1

0.2

41.0

59.3

19.2

2.4

2360

F28

2115

5.5

0.1

5.3

54.8

49.3

0.7

670

F100

2340

0.2

0.1

5.7

13.0

1.2

0.7

740

L1011*

8025

7.3

0.3

29.7

112

65.4

2.5

2540

SAAB 340945

1.4(E)

0.03(E)

0.3(E)

22.1(E)

12.7(E)

0.3(E)

300(E)

Tupolev 154

6920

8.3

0.2

14.0

116.81

75.9

2.2

2190

Concorde

20290

10.7

0.6

35.2

385

96

6.4

6420

GAjet

2150

0.1

0.1

5.6

8.5

1.2

0.7

680

Source: ICAO (1995).
(a) Except where indicated, values are for world fleet weighted LTO fuel and emissions performance. The average age of aircraft inservice is 10-20 years old. Values for aircraft types marked with a * are specific to older types with poorer emissions performance.
Aircraft can be equipped with different engines.
(b) Assuming 10% of total VOC emissions in LTO cycles are methane emission (Olivier, 1991).
(c) Estimates based on Tier 1 default values.
(d) The sulphur content of the fuel is assumed to be 0.05%.
(E) indicates that the figure is based on estimations.

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EMISSION FACTORS OF NOx FOR VARIOUS AIRCRAFT AT CRUISE LEVELS
AircraftEmission Factor for NOx (g/kg)
ANCAT

NASA

Average

A300

NAV

14.4

NAV

A310

11.5

13.6

12.5

A320

11.7

12.1

11.9

BAC 1-11

7.1

9.3

8.2

BAe 146

6.7

7.7

7.2

B727

8.0

8.7

8.4

B737-200

6.8

7.7

7.3

B737-400

8.3

9.6

9.0

B747-200

16.7

14.2

15.5

B747-400

15.8

13.9

14.9

B757

13.1

12.6

12.9

B767

10.0

12.2

11.1

DC8

12.4

5.6

9.0

DC9

7.6

8.1

7.9

DC10

17.5

13.2

15.4

F28

8.5

8.5

8.5

F100

8.4

6.4

7.4

MD80

8.3

10.6

9.5

TU154

NAV

8.7

NAV

Concorde

19.9

NAV

NAV

GAjet

6.7

NAV

NAV

Source: Gardner et al. (1997) and Baughcum et al. (1996).

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TABLE 1-52
DEFAULT EMISSION FACTORS AND FUEL CONSUMPTION FOR AIRCRAFT(LTO EMISSION FACTORS ARE GIVEN ON A PER AIRCRAFT BASIS)
Domestic
Fuel
Consumption

Emission Factors
CO2

CH4 (a)N2O(b)NOx

CO

NMVOC(a)SO2(c)

LTO
average fleet(kg/LTO)

850

2680

0.3

0.1

10.2

8.1

2.6

0.8

LTO
old fleet(kg/LTO)

1000

3150

0.4

0.1

9.0

17

3.7

1.0

3150

0

0.1

11

7

0.7

1.0

Cruise(kg/t of fuel)International
Fuel
Consumption

Emission Factors
CO2

CH4 (a)N2O(b)NOx

CO

NMVOC(a)SO2(c)

LTO
average fleet(kg/LTO)

2500

7900

1.5

0.2

41

50

15

2.5

LTO
old fleet(kg/LTO)

2400

7560

7

0.2

23.6

101

66

2.4

3150

0

0.1

17

5

2.7

1.0

Cruise(kg/t of fuel)Note: The emission factors were calculated as weighted averages for a number of typical aircraft. For domestic traffic, theaverage fleet is represented by Airbus A320, Boeing 727, Boeing 737--400 and Mc Donald Douglas DC9 and MD80 aircraft.
The old fleet is represented by Boeing B737 and McDonald Douglas DC9. For international traffic, the average fleet isrepresented by Airbus A300, Boeing B767, B747 and McDonald Douglas DC10, whilst the old fleet is represented by the
Boeing B707, Boeing B747 and McDonald Douglas DC8. The data for LTO are shown in Table 1-50. Cruise data were takenfrom Wuebbles et al. (1993). The emission factors for cruise are considered as the best available default factors to date.
(a) For CH4 and NMVOC it is assumed that the emission factors for LTO cycles be 10% and 90% of total VOC, respectively(Olivier, 1991). Studies indicate that during cruise no methane is emitted (Wiesen et al., 1994).
(b) Estimates based on Tier 1 default values.
(c) Sulphur content of the fuel is assumed to be 0.05% for both LTO and cruise activities.

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1.6

Fugitive Emissions: Overview
During all of the stages from the extraction of fossil fuels through to their final use theescape or release of gaseous fuels or volatile components or absorbed gases may occur.
The methodologies for the estimation of these emissions (mostly methane) are presented
in the sections which follow and are limited to activities conducted within the confines ofthe energy industries. Emissions from the use of road vehicle fuels are covered underfuel combustion. Emissions from solvents use are estimated within Chapter 3 but
emissions arising from the manufacture of solvents within refineries are subsumed within
the estimation of emissions from refineries in Section 1.8 Fugitive Emissions from Oil andNatural Gas Activities.

1.7

Fugitive Emissions from Coal Mining and
Handling
1.7.1 Overview
This section covers fugitive emissions of greenhouse gases (GHGs) from production,
processing, handling and utilisation of coal. Intentional or unintentional releases of gases
such as methane in mining are included here, as are emissions from inadvertent
combustion of coal in coal mine fires. By far the most important component of thissubcategory is methane (CH4) emissions from the mining and handling of coal. The bulkof this section, therefore, deals with these emissions. Two other fugitive emission
sources are discussed briefly at the end of the section. These are burning coal mines andwaste piles, which emit CO2, and SO2 scrubbing, which is also a source of CO2. There
are very likely other fugitive emissions associated with the coal fuel cycle. If importantsources are identified, these will be considered for inclusion in future editions of the
Guidelines.

1.7.2 CH4 from Coal Mining and Handling
1.7.2.1

GENERAL METHODOLOGY

The process of coal formation, commonly called coalification, inherently generates
methane and other by-products. The formation of coal is a complex physio-chemical
process occurring over millions of years. The degree of coalification (defined by the rankof the coal) determines the quantity of methane generated and, once generated, theamount of methane stored in the coal is controlled by the pressure and temperature of
the coal seam and by other, less well-defined characteristics of the coal. The methane
will remain stored in the coal until the pressure on the coal is reduced, which can occur
through the erosion of overlying strata or the process of coal mining. Once the methane
has been released, it flows through the coal toward a region of lower pressure (such as acoal mine) and into the atmosphere (Boyer, 1990). Methane emissions from coal mining
in 1990 contributed an estimated 23 to 39 Tg of global methane emissions (US EPA,
1993a; CIAB, 1992; Airuni and Zeidenvarg, 1992).
The amount of CH4 generated during coal mining is primarily a function of coal rank anddepth, gas content, and mining methods, as well as other factors such as moisture. Coal

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rank represents the differences in the stages of coal formation and depends on thepressure and temperature history of the coal seam; high coal ranks, such as bituminous
coal, contain more CH4 than low coal ranks, such as lignite. Depth is important because
it affects the pressure and temperature of the coal seam, which in turn determines how
much CH4 is generated during coal formation. If two coal seams have the same rank, thedeeper seam will hold larger amounts of CH4 because the pressure is greater at lower
depths, all other things being equal. As a result, the methane emission factors forsurface-mined coal are assumed to be lower than for underground mining.
In most underground mines, methane is removed by ventilating large quantities of air
through the mine and exhausting this air (typically containing a concentration of 1 percent methane or less) into the atmosphere. In some mines, however, more advanced
methane recovery systems may be used to supplement the ventilation systems and ensuremine safety. These recovery systems typically produce a higher concentration product,
ranging from 35 to 95 per cent methane. In some countries, some of this recovered
methane is used as an energy source, while other countries vent it to the atmosphere.
Recent technological innovations are increasing the amount of medium- or high-quality
methane that can be recovered during coal mining and the options available to use it.
Thus, methane emissions could be reduced from this source in the future.
In surface mines, exposed coal faces and surfaces, as well as areas of coal rubble createdby blasting operations, are believed to be the major sources of methane. As in
underground mines, however, emissions may come from the overburden (in limited cases
where these strata contain gas), which is broken up during the mining process, andunderlying strata, which may be fractured and destressed due to removal of theoverburden. Because surface-mined coals are generally lower rank and less deeply
buried, they do not tend to contain as much methane as underground-mined coals. Thus,
emissions per tonne of coal mined are generally much lower for surface mines. Research
is underway in the United States and elsewhere to increase the understanding of CH4
emissions from surface mines (Kirchgessner et al., 1993; USGS, 1993).
A portion of the CH4 emitted from coal mining comes from post-mining activities such ascoal processing, transportation, and use. Coal processing involves the breaking, crushing,
and thermal drying of coal, making it acceptable for sale. Methane is released mainly
because the increased surface area allows more CH4 to desorb from the coal.
Transportation of the coal contributes to CH4 emissions, because CH4 desorbs directlyfrom the coal to the atmosphere while in transit (e.g., in railroad cars). Use of
metallurgical coal also emits methane. For instance, in metallurgical coke production, coalis crushed to a particle size of less than 5 mm, vastly increasing the surface area of thecoal and allowing more CH4 to desorb. During the coking process, methane, carbon
monoxide, and other volatile gases are released. In modern coke ovens, this gas is
typically collected and used as a fuel source, but in older coke ovens, particularly thoseused in less developed regions, coke gas is vented to the atmosphere (Boyer et al., 1990;
coke production is covered in Chapter 3).
Some methane is also released from coal waste piles and abandoned mines. Coal waste
piles are comprised of rock and small amounts of coal that are produced during mining
along with marketable coal. There are currently no emission measurements for thissource. Emissions are believed to be low, however, because much of the methane would
likely be emitted in the mine and the waste rock would have a low gas content comparedto the coal being mined. Emissions from abandoned mines may come from unsealed
shafts and from vents installed to prevent the build-up of methane in mines. There is very
little information on the number of abandoned mines, and no data are currently available
on emissions from these mines. Most available evidence indicates that methane flow rates
decay rapidly once deep mine coal production ceases (Williams and Mitchell, 1992;

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Creedy, 1991). In some abandoned mines, however, methane can continue to bereleased from the surrounding strata for many years. In Belgium, France, and Germany,for example, several abandoned mines are currently being used as a source of methane
which is being added to the gas system (Smith and Sloss, 1992; KfA, 1993). Due to theabsence of measurement data for both coal waste piles and abandoned mines, noemissions estimates have been developed for these sources.
Review of Previous Methane Emission Estimation Studies
Over the years, a variety of methane emissions estimates have been developed for coalmining, as shown in Table 1-53. As the table shows, the variation in estimates has beenquite large, although more recent studies are showing more similar results. Many of theemission studies conducted to date have confronted difficulties in developing estimation
methodologies and these have resulted in the widely varying estimates and large
uncertainties. These difficulties include:•

Absence of data on which to base estimates: Many studies were developed
without access to detailed data on methane emissions associated with various
components of the coal cycle. For certain sources such as surface mines and postmining activities, moreover, reliable emissions measurements are still lacking.

•Use of national data to develop global estimates: Some studies have reliedon data from a single country to estimate global methane emissions from coalmining. This approach can introduce large errors into the estimates, due to thedifficulty of generalising from one country's coal characteristics and mining
conditions to those of other countries. Mining experience has shown that there are
frequently significant differences in methane emission factors within countries, coalbasins, and even coal mines for a variety of geological and other reasons.

•

Failure to include all possible emission sources: Some studies prepared todate have only estimated underground coal mining emissions from ventilation
systems and have not included emissions from degasification systems, or post-mining
emissions. In addition, many estimates have assumed emissions from surface mines
to be negligible and have not included this source. At this point, moreover, there
are still potential emission sources, such as abandoned mines, for which emissions
cannot be estimated due to the absence of necessary data.

•

Over-reliance on statistical estimation methodologies: Several studies haveestimated global emission factors using statistical models that relate methane
emissions to various coal properties. For the most part, these models have provenunreliable when estimates are compared to those developed using more detailed
country-specific information.
The principal problem with using statisticalmethodologies is the number of variables that can affect methane emissions. Mining
experience has shown that a complete understanding of methane emissions requires
detailed examination of coal and geological characteristics and that methane
emissions can be highly variable within mines, basins and countries. Collecting
comprehensive data and developing statistical models that can reliably predict
emissions on a global basis is thus very difficult.

In general, the results of the more recent country-specific and global methane emission
studies are likely to be more reliable than previous efforts. For several of the major coalproducing countries, for example, detailed data on methane emissions from undergroundmine ventilation and degasification systems are reported to central institutes and are
publicly available. More recent studies have been able to use these data in preparing andvalidating their estimates of methane emissions from underground mines. Data are still

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lacking on emissions from surface mines and post-mining activities, thus even the emission
estimates from more recent studies should be considered uncertain.
Suggested Emission Estimation Methods
Methane emission estimates should be developed for the three principal sources ofmethane emissions: underground mines, surface mines, and post-mining activities. To
assist in developing these estimates, the IPCC recommends use of a "tiered" approach forestimating emissions. For each source, two or more approaches (or "tiers") arepresented for estimating emissions, with the first tier requiring basic and readily available
data and higher tiers requiring additional data. Selection among the tiers will depend
upon the quality of the data available in the country.

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SUMMARY OF EMISSIONS ESTIMATES FROM SELECTED STUDIES
Study Author

Emissions
Estimate

Year of Estimate

Methodological Issues(Tg)
Koyama (1963)

20

1960

Hard coal only; no emissions estimates for surface
mining or post-mining activities. 1960 coalproduction data.

Hitchcock & Wechsler (1972)

8 - 281967

Post-mining not included; source of emission
factors, particularly low end, unspecified. 1967
coal production data.

Seiler (1984)

30

1975

Crutzen (1987)

34

NA

Source of emission factors unclear. Hard coal
only; no emissions estimates for surface mining or
post-mining activities.

Okken & Kram (1989)

15 - 45

NA

Source of emission factors unclear. Hard coal only;
no emissions estimates for surface mines or postmining activities.

Zimmermeyer (1989)

24

NA

Only underground mining considered; noemissions estimates for surface mines or postmining activities.

Seltzer & Zittel (1990)

23

NA

Barns & Edmonds (1990)

25

1986

Boyer et al. (1990)

33 - 64

1988

Hargraves (1990)

29

NA

Method based on current methane production
rates due to continued coalification.

Airuni and Zeidenvarg (1992)

28

1990

Methodology unspecified.

CIAB (1992)

24

1990

US EPA (1993c)

23 - 39

1990

Based on Koyama, with 1975 coal production
data.

Adjusted Zimmermeyer by: (1) including surface
mines; (2) assuming that 15 per cent ofunderground mining emissions (3.6 Tg) not
emitted to the atmosphere due to methane
utilisation.
Assumed mathematical relationship between coalrank and depth and that in-situ methane content
was equal to the mining emission factor.
Statistical approach related methane emissions toin situ methane content. Correlation based on US
data only. Large uncertainty in application of
results for global estimates.

Country specific data used where available forunderground mines. Surface and post-mining
emissions developed using low emission
assumptions. No uncertainty analysis.
Country specific data used where available forunderground mines. Global average emission
factors for rest of countries for undergroundmines and for all surface mining and post-mining
emissions.

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1.7.2.2

UNDERGROUND MINING

Methane emissions from underground mines should include estimated emissions fromventilation systems and from degasification systems, if any of a country's mines use
degasification systems to supplement ventilation. In the approaches outlined below,
methods of estimating emissions from both of these sources are presented.
Three possible approaches are suggested by the IPCC, with the choice among them
depending upon the availability of data and the degree to which coal mining is considereda significant source of emissions by particular countries. Two of the methods, the“Global” and the “Country or Basin Average” methods are essentially identical in form;
only the degree of detail and specificity in choice of emission factor(s) differs. The third,“Mine Specific” method relies on the assembly of methane emission measurements taken
at coal mines. In the first two methods, Tiers 1 and 2, ranges of emission factors are
given in terms of m3 CH4/tonne of coal produced. The structure of the estimation is
simplyEmissions (Gg CH4) = Emission Factor (m3 CH4 / tonne)
x tonnes of coal produced
x Conversion Factor (Gg/106m3)
A single value from the range of emission factors should be used to prepare the emissions
estimate. The relevant coal production figure will be that for the country or the coalbasin depending upon the method selected. Factors are given in the table below which
permit the conversion of the volume emitted to mass.
For those countries with comparatively large methane emissions from coal mining, theuse of more detailed estimation methodologies may be warranted. In countries
producing smaller quantities of coal, however, the most simple approach may provide a
reasonably accurate first approximation of CH4 emissions from underground mines.
Tier 1: Global Average Method
The simplest method for estimating methane emissions is to multiply underground coalproduction by a factor drawn from a range of factors representing global average
emissions from underground mining, including both ventilation and degasification systememissions. This method may be selected in cases where total coal production fromunderground mines is available but more detailed data are not. The Tier 1 Equation isshown below.

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TIER 1: GLOBAL AVERAGE METHOD – UNDERGROUND MINES

CH4 Emissions (Gg) = CH4 Emission Factor (m3 CH4/tonne of coal mined)
x Underground Coal Production (Mt)x Conversion Factor (Gg/106 m3)
Where:
 the Emission Factor should be chosen from the following range

Low CH4 Emission Factor = 10 m3/tonne
High CH4 Emission Factor = 25 m3/tonne
 Conversion Factor converts the volume of CH4 to a weight measure andis the density of methane at 20°C and 1 atmosphere, namely:
0.67 Gg / 106 m3
The IPCC recommends revised global average emission factors of 10 to 25 m3/tonne ofcoal mined (not including emissions from post-mining activities which should be calculated
separately). This range reflects the findings of various country studies, as shown in
Table 1-54. As more detailed emissions data are published by various countries, thefactors can be further revised, if necessary.

TABLE 1-54
ESTIMATED UNDERGROUND EMISSION FACTORS FOR SELECTED COUNTRIESCountry

Emission Factors(m3/tonne)

SourceFormer Soviet Union

17.8 - 22.2

US EPA, 1993c

United States

11.0 - 15.3

US EPA, 1993a

Germany (East & West)

22.4

Zimmermeyer, 1989

United Kingdom

15.3

BCTSRE, 1992

Poland

6.8 - 12.0

Pilcher et al., 1991

Czechoslovakia

23.9

Bibler et al., 1992

Australia

15.6

Lama, 1992

Tier 2: Country or Basin Specific Method
The suggested Tier 2 approach – called the "Country or Basin Specific Method" – can beused to refine the range of emission factors used for underground mining by
incorporating some additional country or basin-specific information. Basically, thismethod enables a country with limited available data to determine a more appropriate
and probably narrower range of emission factors for their underground mines. For many
countries, it is expected that this range will fall within the global average emission factor
range of 10 to 25 m3/tonne. The range of possible emission factors is not constrained
under the Tier 2 approach, however, and some countries may find that theirunderground mining emission factors lie outside the global average emission factor range.
The calculation procedure is identical to that described in Tier 1.
To implement the Tier 2 approach, national experts must examine measurement datafrom at least a limited number of underground coal mines in their country or region.
Using this data, either statistical analysis or expert judgement should be applied to

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develop a reasonable range of emission factors for the country or region.27 Making thisestimate will require judgement on the part of the estimator as to the adequacy of theavailable data and its uncertainty. If sufficient expertise is not available to make suchjudgements, it is recommended that the Tier 1 approach (the Global Average Method) be
used instead.
In some cases, measurement data on emissions from mines may be unavailable but acountry will still seek to develop a narrower estimate based on other types of available
data. In such cases, a country may seek to develop a simple emissions model based on
physical principles or make judgements based on an evaluation of available data. Amongthe key types of data that should be considered in such a model or evaluation are:•the gas content of the coal, which contributes to the total amount of methane
available for emission during mining;•

the amount of coal within the strata above and below the mined coal seam, which
also contributes to the total amount of methane available for emission during mining;and,•the method of mining, which determines the amount of ground that is disturbed bymining the coal and the extent to which the mining process liberates methane
contained in the mined coal seam and in the strata surrounding it.

It should be noted that while the Tier 2 approach can provide some additional
information about methane emissions in a particular country or coal basin, the estimates
will still be quite uncertain because of the absence of comprehensive and reliable
emissions data. This approach should thus be used only in cases where there is a strong
need to make an estimate drawn from a narrower range than the Tier 1 (Global Average
Method) and not enough data are available to prepare an estimate using the Tier 3 (MineSpecific Method) described in the next section. It should further be noted that an
estimate from the narrower range will not necessarily be more accurate than thatdeveloped under Tier 1.
In all cases where the Tier 2 approach is used, a detailed discussion of the types of data
available and the manner used to determine the refined range of emission factors should
be presented, so as to allow for the independent verification of the estimate and ensurecomparability with estimates being prepared by other countries.
Tier 3: Mine Specific Method
Because methane is a serious safety hazard in underground mines, many countries havecollected data on methane emissions from mine ventilation systems, and some also collectdata on methane emissions from mine degasification systems. Where such data are
available, the more detailed Tier 3 approach – called the "Mine Specific Method" – should
provide the most accurate estimate of methane emissions from underground mines.
Since these data have been collected for safety, not environmental reasons, however, it isnecessary to ensure that they account for total emissions from coal mines. The key
issues that should be considered when using mine safety data, as well as therecommendations of the IPCC for resolving them, are shown in Table 1-55.

27 If measurement data is available for most or all or a country's underground coalmines, the Tier 3 approach – called the "Mine Specific Method" – should be used toestimate emissions.

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Treatment of Methane Utilisation
All of the methods described above, with the possible exception of the Mine SpecificMethod, assume that all of the methane liberated by mining will be emitted to theatmosphere. In many countries, however, some of the methane recovered by minedegasification systems is used as fuel instead of being emitted. Wherever possible, theemission estimates should be corrected for the amount of methane that is used as fuel, by
subtracting this amount from total estimated emissions.
In several countries, data on the disposition of methane recovered by degasification
systems (i.e., whether it is used or emitted to the atmosphere) can be obtained from thecoal industry or energy ministries. Poland, for example, reports that its minedegasification systems recovered 286 million m3 of methane in 1989, of which 201 million
m3 was used and the remaining 85 million m3 was emitted to the atmosphere (Polish
Central Mining Institute, 1990). Regardless of the method used to develop the emissions
estimates, the Polish emission estimate should be adjusted to reflect the use of methaneby subtracting 201 million m3 from total emissions.
In some countries figures for the quantity of gas recovered from mines may not be
available from the mining industry. Nevertheless estimates may be constructed if theusers of the gas are known and they are able to give data for their consumption.
Consumption may also be inferred if it is known that the gas is used to fuel a particularplant of a known capacity (e.g. if the methane is used to fuel a gas turbine of a knownsize).

TABLE 1-55
KEY ISSUES FOR CONSIDERATION WHEN USING TIER 3 – MINE SPECIFIC METHODISSUEDESCRIPTIONRECOMMENDATION

Where and how are ventilation
system emissions monitored?

When used to develop overall
methane emission estimates, theoptimal location for ventilation air
monitors is at the point where
ventilation air exhausts to theatmosphere.

If ventilation emissions are not monitored at the
point of exhaust, emission data should becorrected based on estimated additional
methane emissions between the point of
measurement and the point of exhaust to theatmosphere.

Are ventilation system emissions
monitored and/or reported for allmines?

In some countries, emissions are only
reported for "gassy mines".

Estimates should be developed for non-gassy
mines as well. Estimates can be prepared using
information about the definitions of gassy andnon-gassy mines and data on the total number ofmines and the coal production at these mines.

Are methane emissions fromdegasification systems reported?

Some countries collect and reportmethane emissions from ventilationand degasification systems, whileothers only report ventilation systememissions. Both emission sourcesmust be included in emissions
estimates.

If degasification system emissions are notincluded, those mines with degasification systems
should be identified and estimates prepared onemissions from their degasification systems.
Emissions estimates can be based on knowledge
about the efficiency of the degasification system
in use at the mine or the average efficiency ofdegasification in the country.

The sources of any adjustments to emissions that are made to reflect the utilisation of
methane should be clearly specified, to permit the independent verification of theemissions estimates. In the absence of data, estimated adjustments for the use of
methane should not be undertaken.

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1.7.2.3

SURFACE MINING

Two possible approaches for estimating methane emissions from surface mining aresuggested by the IPCC. For the most part, these approaches resemble those developedfor underground mining, but the results will be much more uncertain due to the absenceof emissions data. Methane emissions from surface mining are assumed to arise fromtwo sources: the coal mined and the surrounding strata exposed during the mining
process. In the Tier 1 approach, (Global Average Method) the separation of thesesources is ignored and a single emission factor is used. In the Tier 2 approach (Country
or Basin Specific Method), emission factors for each source are required. If emissions
measurements are developed in the future, it should be possible to refine thesemethodologies.
Tier 1: Global Average Method
As for underground mining, the simplest Tier 1 approach for surface mines – called the"Global Average Method" – is to multiply surface coal production by an emission factor
selected from a global range, within which most emission factors are believed to lie.
EQUATION 2
TIER 1: GLOBAL AVERAGE METHOD – SURFACE MINES

CH4 Emissions (Gg) = CH4 Emission Factor (m3 CH4/tonne of coal mined)
x Surface Coal Production (Mt)x Conversion Factor (Gg/106 m3)
Where:•

the Emission Factor should be chosen from the following range:
Low CH4 Emission Factor = 0.3 m3/tonne
High CH4 Emission Factor = 2.0 m3/tonne•

Conversion Factor converts the volume of CH4 to a weight measure,and is the density of methane at 20°C and 1 atmosphere, namely:
0.67 Gg/ 106 m3

In the original IPCC methodology, an average emission factor of 2.5 m3/tonne wasrecommended (OECD, 1991), based on the results of Boyer et al. (1990) and including
emissions from post-mining operations. Based on more recent analyses and additional
studies, a revised emission factor range of 0.3 to 2.0 m3/tonne is recommended by the
IPCC, not including post-mining emissions (US EPA, 1993c; CIAB, 1992; BCTSRE, 1992;
CMRC, 1990; Kirchgessner et al., 1993).
Given the lack of information and measurements on methane emissions from surface
mines, this range must be considered extremely uncertain, and it should be refined in the
future as more data become available.
Tier 2: Country or Basin Specific Method
A second tier estimation of methane emissions – called the "Country or Basin SpecificMethod" – can be used if additional information is available on in-situ methane content andother characteristics of a country's surface-mined coals. This approach enables a country
to develop emission factors that better reflect specific conditions in their countries.

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Depending on the degree of detail desired, emissions can be estimated for specific coalbasins or countries, using the equation below.
EQUATION 3
TIER 2: COUNTRY OR BASIN SPECIFIC METHOD – SURFACE MINES

CH4 Emissions (Gg) = [In-Situ Gas Content (m3 CH4/tonne)
x Surface Coal Production (Mt)x Conversion Factor (Gg/106 m3)]+

[Assumed Emission Factor for Surrounding Strata(m3 CH4/tonne)
x Surface Coal Production (Mt)x Conversion Factor (Gg/106 m3)]

Where:•

In-Situ Gas Content and Assumed Emission Factor for Surrounding
Strata are described in the text.

•

Conversion Factor converts the volume of CH4 to a weight measureand is the density of methane at 20°C and 1 atmosphere, namely:
0.67 Gg /106 m3

In Equation 3, In-Situ Gas Content represents the methane actually contained in the coal
being mined, as determined by measuring the gas content of coal samples. Average values
for a coal mine, coal basin or country could be developed, depending on the level of detailin the estimate. For surface mines, unlike underground mines, it is frequently assumed
that all of the methane contained in the coal is released during mining and that postmining emissions from surface-mined coals are effectively zero (BTSCRE, 1992; CIAB,
1992; CMRC, 1990). Some countries may choose to modify this assumption based on
their specific conditions. Care should be taken, however, to ensure that any emissions
assumed to occur during post-mining activities are subsequently estimated.
Assumed Emission Factor for Surrounding Strata represents the possibility that moremethane will be emitted during surface mining than is contained in the coal itself becauseof emissions from the strata below (or in limited cases, above) the coal seam. Somecountries have assumed that there are no emissions from surrounding strata associatedwith surface-mined coals (BTSCRE, 1992; CMRC, 1990).
However, if available
information indicates that there are gas-bearing strata surrounding the mined coal seamand that these strata are emitting their gas in conjunction with the mining, countries
should include these emissions in their estimates.
Emission factors for the surrounding strata can be developed using one of two
approaches. Ideally, the assumed emission factor should be based on an evaluation of thegas content of the surrounding strata and verified by measurements. If such data areunavailable, an alternative method of developing an emission factor is to assume thatsome multiple of the gas content of the mined coal is emitted by the surrounding strata.
It should be noted, however, that the alternative approach is highly speculative given thelack of data upon which to base such an assumption.

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1.7.2.4

POST-MINING

Like surface mining emissions, there are currently few measurements of methane
emissions from post-mining activities. In fact, many past studies have overlooked thisemission source, while others have developed only rudimentary estimation
methodologies. Two possible approaches for estimating emissions from post-mining
activities are recommended by the IPCC.
Tier 1: Global Average Method
For the most simple estimates, a global average emission factor can be multiplied by coalproduction for underground and surface mining, as shown in the equation below. It is
important to distinguish between underground- and surface-mined coals because the gas
contents are likely to be very different and hence emissions could vary significantly.
EQUATION 4
TIER 1: GLOBAL AVERAGE METHOD – POST-MINING ACTIVITIESUnderground CH4 Emissions (Gg) = CH4 Emission Factor (m3 CH4/tonneof coal mined)
x Underground Coal Production (Mt)x Conversion Factor (Gg/106 m3)
Surface CH4 Emissions (Gg) =CH4 Emission Factor (m3 CH4/tonneof coal mined)
x Surface Coal Production (Mt)x Conversion Factor (Gg/106 m3)

Where:•

Underground CH4 Emission Factors are in the range of:
0.9 to 4.0 m3/tonne•

Surface CH4 Emission Factors are in the range of:
0 to 0.2 m3/tonne•

Conversion Factor converts the volume of CH4 to a weight measureand is the density of methane at 20°C and 1 atmosphere, namely:
0.67 Gg/106 m3

Underground-Mined Coals:
The IPCC recommends emission factors of 0.9 to
4.0 m3/tonne for underground-mined coal, based on recent studies (CIAB, 1992; BCTSRE,
1992; US EPA, 1993c).
Surface-Mined Coals: Emission factors of 0 to 0.2 m3/tonne are recommended by the
IPCC for post-mining activities involving surface-mined coal (CIAB, 1992; CMRC, 1990;
US EPA, 1993c).
Tier 2: Country or Basin Specific Method
Emissions estimates can be refined if additional data are available on coal characteristics.
This method may be preferable if higher tier methods have been used to estimate
emissions from underground and surface mines. The equation below summarises theapproach for preparing refined emission estimates.

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TIER 2: COUNTRY OR BASIN SPECIFIC METHOD – POST-MINING ACTIVITIESa) Underground CH4 Emissions (Gg) = In-Situ Gas Content (m3 CH4/tonne)x Underground Coal Production (Mt)x Fraction of Gas Released During
Post-Mining Activities (%)
x Conversion Factor (Gg/106 m3)

When Necessary:b) Surface CH4 Emissions (Gg) =In-Situ Gas Content (m3 CH4/tonne)
x Surface Coal Production (Mt)x Fraction of Gas Released During
Post-Mining Activities (%)
x Conversion Factor (Gg/106 m3)

Where:• In-Situ Gas Content and Fraction of Gas Released During Mining aredescribed in the text
• Conversion Factor converts the volume of CH4 to a weight measure andis the density of methane at 20°C and 1 atmosphere, namely:
0.67 Gg/106 m3

In-Situ Gas Content represents the methane actually contained in the coal being mined, as
determined by measuring gas contents in coal samples. Average values for a coal mine,coal basin or country could be developed, depending on the level of detail in the estimate.
Fraction of Gas Released During Post-Mining Activities represents the percentage of thein-situ gas content that is assumed to be emitted during post-mining activities. There arethree key issues related to the estimation of this fraction:•

For Surface-Mined Coal: In most cases, if the Tier 2 approach is used to estimate
methane emissions from surface mines, post-mining emissions from surface-minedcoals are assumed to be zero. In these cases, the use of Equation 5(b) is
unnecessary and countries should be careful to avoid double counting. However, if
a country has not assumed that all of the methane contained in surface-mined coal isreleased during mining, Equation 5(b) should be used to estimate post-mining
emissions and the value selected for "Fraction of Gas Released During Post-Mining
Activities" should be consistent with the emission factor selected to estimate
emissions during surface mining.

•

For Underground-Mined Coal: The assumed fractions for underground mining will
be based on information about coal permeability, desorption rates, mining methods
and other factors. Recent studies have assumed that 25 to 40 per cent of the in-situ
CH4 content of underground mined coal is emitted during post-mining activities(US EPA, 1993a; BCTSRE, 1992).

•

Fraction of Methane Not Emitted: It is currently assumed that all of the CH4
contained in mined coal will be emitted to the atmosphere, although it is possiblethat a fraction could remain in the coal until the point of combustion and be burned
instead of emitted. At this time, estimates of the extent to which this may be the

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case have not been developed. If countries have such information, however, they
could further incorporate this factor into Equation 5.
Total Emissions from Coal Mining Activities
Total methane released as a result of coal mining activities will be the summation ofemissions from underground mining (ventilation and degasification systems), surface
mining, and post-mining activities. The IPCC recommends that emissions be estimatedfor each of these categories, in tonnes of CH4, then aggregated to determine total
national methane releases. To the extent that methane that would otherwise have beenreleased to the atmosphere is recovered and used as fuel, the recovered quantity and its
use should be reported and the quantity subtracted from the emission total.
Availability and Quality of Activity Data
Data are readily available to develop general emissions estimates using the Tier 1
approach – the Global Average Methods – for underground, surface mining as well as
post-mining activities. For these estimates, the only data required are country statistics
on underground and surface coal production, which are available from domestic sources,
such as energy ministries, or from the OECD/IEA, which publishes Coal Information(OECD/IEA, 1996).
The IPCC recommends that countries involve their coal mining personnel in thedevelopment of emissions estimates as much as possible, because of the improved
accuracy of emissions estimates prepared with more detailed coal and mining data. The
availability and quality of data collected by mining personnel for mine safety purposes
should be assessed on a case-by-case basis, however, to ensure that it can be usedappropriately for preparing emissions estimates.
The IPCC further recommends that future efforts attempt to better characterise thefactors affecting methane emissions from coal mining for those countries and emission
sources with limited data, so as to develop more refined emission factors. Specificactivities should include:•

Obtaining more data on coal and geological characteristics in selected coal-producing
countries;•

Monitoring emissions from surface mines and post-mining activities; and,•

Monitoring emissions from closed or inactive mining operations, and some otherpotential methane sources, such as mine water.

1.7.3

1.7.3.1

CO2 Emissions From Coal Mining and
Handling
BURNING COAL DEPOSITS AND WASTE
PILESMarland and Rotty (1984) estimated that burning of coal in coal deposits is less than
0.3 per cent of total coal produced and that burning of all coal in waste banks in the
United States over a ten year period would represent less than 1 per cent of US coalconsumption. Subsequently, they chose to ignore these emissions.
If these sources are estimated, the amount of coal burned in waste piles and coal deposits
must be specified along with an emission factor that represents the percentage of coal

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that is carbon times the percentage of carbon oxidised. We suggest an arbitrary value of
50 per cent of the carbon present in the coal to represent this emission factor; this value
would be highly variable from one country to another and one site to another. This
assumption of 50 per cent for an emission factor should be evaluated to determine its
validity. The formula for calculating these emissions would be:
EQUATION 6

Emissions from Coal Burning (Gg C) = Quantity of Coal Burned (103 t)
x Emission Factor
Where:•The Emission Factor is:

Percentage of Carbon in Coalx Percentage of Carbon Oxidised;(and the default value is 50%)

Note that other GHGs such as N2O, CO, NOx, etc. are also emitted from combustion ofcoal wastes.

1.7.3.2

SO2 SCRUBBING

When SO2 scrubbing (or flue gas desulphurisation) technology is used in conjunction withcombustion of coal, the process, which removes sulphur dioxide from the flue gas, also
releases CO2 from the chemical reactions during the process. This can be considered afugitive emission resulting from coal use. Typically, calcium carbonate reacts with sulphuroxides in flue gas to produce calcium sulphate and carbon dioxide. Marland and Rotty(1984) suggest that CO2 emissions from SO2 scrubbing are small enough to be ignored in
global calculations. However, for completeness, some national experts may wish toinclude this subcategory.
To estimate carbon emissions from SO2 scrubbing, the approach is derived from Grubb(1989) with slight modifications. In Grubb's approach, carbon emissions would equal the
total amount of coal combusted in plants equipped with scrubbers times the fraction ofsulphur by weight in the coal, adjusted for the differences in molecular weight between
carbon and sulphur (12/32). Since this procedure assumes that all of the sulphur isremoved, it should be adjusted by the sulphur removal efficiency of the desulphurisation
process (an average removal efficiency of 90 per cent is suggested). The formula for
calculating these emissions would be:
EQUATION 7

Emissions from SO2 Scrubbing (Gg C) = Total Coal Consumption (103 t)
x Fraction burned in plants equipped with scrubbers(%)
x Average Sulphur Content of Coal in these plants (%)
x Sulphur Removal Efficiency (default value is 90%)x 12/32 (i.e., the Carbon/Sulphur Ratio)

Finally, to convert from carbon emissions (in Gg) into CO2 emissions (in Gg), it isnecessary to multiply by 44/12, the molecular weight ratio of CO2 to C.

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1.8

Fugitive Emissions from Oil And Natural
Gas Activities
1.8.1 Overview
This section covers fugitive emissions of greenhouse gases (GHGs) from oil and natural
gas activities. The category includes all emissions from the production, processing,transport and use of oil and natural gas, and from non-productive combustion. It
excludes use of oil and gas or derived fuel products to provide energy for internal use, inenergy production processing and transport. The latter are considered fuel combustion
and treated in an earlier section of this chapter. Fugitive emissions do include, however,
emissions which result from the combustion of natural gas during flaring operations.
By far the most important components of this subcategory are methane emissions fromoil and gas production, and from all aspects of natural gas activities. The majority of thissection identifies and describes different methane emission sources from oil and naturalgas, and presents a default methodology to estimate these emissions on a national level.
The basis for estimating methane emissions from oil and gas is, however, weak for mostregions at this time. Only a few detailed studies of emissions rates have been performed.
Better emissions data that take into account region- and country-specific factors areneeded. Information currently available indicates that gas production and transmission in
the former USSR and Eastern Europe are by far the most important sources, accounting
for perhaps 50 per cent of global CH4 emissions from oil and natural gas. Because thedata are so limited at present, global and regional estimates of CH4 emissions from thissource category should be considered highly uncertain.
The IPCC/OECD/IEA programme has not yet addressed the indirect GHGs (including
NMVOCs) in detail. However, the Joint EMEP/CORINAIR method offers both asimplified and a more detailed approach to the estimation of ozone precursors and SO2.
Considerable information has been obtained in other national and international emissions
inventory programmes for NMVOCs because of the importance of these gases for local
and regional (as well as global) pollution. References to some of the available sources ofemission factor data and other information for calculating emissions from this category
are provided in the last subsection of this section.
Background
Fugitive emissions of methane from oil and gas activities probably account for about 30 to
60 Tg per year of global methane emissions. Sources of fugitive emissions within oil andgas systems include: releases during normal operation, such as emissions associated withventing and flaring, chronic leaks or discharges from process vents, emissions during
maintenance, and emissions during system upsets and accidents.

1.8.2 Oil and Natural Gas Activities
Oil and gas activities are divided into three main parts, for this discussion:
1

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Oil and Gas Production: Oil and gas are withdrawn from undergroundformations using on-shore and off-shore wells and are often taken simultaneously
from the same geological formation, and then separated. Gathering lines are
generally used to bring the crude oil and raw gas streams to one or more collection

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point(s) within a production field. Because methane is the major component of
natural gas, leaks or venting from these systems result in methane emissions. Oil
and/or gas are produced in approximately 186 countries world-wide.
2

Crude Oil Transportation and Refining: Crude oil is transported by pipelines
and tankers to refineries where it is stored in tanks for a period of time. Methane ispresent, in varying degrees, in crude oil, and leaks or venting of vapours duringtransport and storage result in methane emissions, particularly from crude oiltankering.
Refineries process crude oil into a variety of hydrocarbon products such as gasoline
and kerosene. During the refining process, dissolved gases are separated some ofwhich may be leaked or vented during processing. Refinery outputs, referred to as"refined products," generally contain negligible amounts of methane. Consequently,
methane emissions are not estimated for transporting and distributing refined
products. Refineries are operated in 102 countries.

3

Natural Gas Processing, Transportation, and Distribution: Natural gas isprocessed to recover heavier hydrocarbons, such as ethane, propane and butane,
and to prepare the “dried” gas for transport to consumers. Most gas is transported
through transmission and distribution pipelines. A small amount of gas is shipped bytanker as liquefied natural gas (LNG). Because for the time being only a small
portion of gas is transported as LNG, emissions from LNG facilities are not included
in default emission methods.
The following are the main processing, transportation, and distribution activities:•

Gas processing plant: Natural gas is usually processed in gas plants to produce
products with specific characteristics. Depending on the composition of theunprocessed gas, a variety of processes may be used to remove most of theheavier hydrocarbons, or condensate, from the gas.
The processed,
marketable, gas is then injected into the natural gas transmission system andthe heavier hydrocarbons are marketed separately. Unintentional leaks ofmethane occur during natural gas processing.

•Transmission pipelines: Transmission facilities are high pressure lines thattransport gas from production fields, processing plants, storage facilities, andother sources of supply over long distances to distribution centres, or large
volume customers. Although transmission lines are usually buried, a variety ofabove-ground facilities support the overall system including metering stations,maintenance facilities, and compressor stations located along the pipeline
routes. These activities use gas from the pipeline as fuel and may emit
methane.

•Distribution systems: Distribution pipelines are extensive networks ofgenerally small diameter, low pressure pipelines. Gas enters distribution
networks from transmission systems at "gate stations" where the pressure is
reduced for distribution within cities or towns. As with transmission pipelines
emissions from leaks or supporting facilities may take place.

1.8.3 Sources of Methane Emissions from Oil andNatural Gas Activities
Emissions from oil and gas activities can be categorised into: (1) emissions during normal
operations; (2) maintenance; and (3) system upsets and accidents. Typically the majorityof emissions are from normal operations.

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