## Emission factors for surface mining

Although measurements of methane emissions from surface mining are increasingly available, they are difficult to make and at present no routine widely applicable methods exist. Data on in situ gas contents before overburden removal are also scarce for many surface mining operations.

The Tier 1 emission factors are shown together with the estimation method in Equation 4.1.7.

Equation 4.1.7 Tier 1: global average method - surface mines

Methane emissions = CH4 Emission Factor •Surface Coal Production • Conversion Factor

Where units are:

Methane Emissions (Gg year- ) CH4 Emission Factor (m3 tonne-1) Surface Coal Production (tonne year-1) Emissions Factor: Low CH4Emission Factor Average CH4 Emission Factor High CH4 Emission Factor Conversion Factor:

This is the density of CH4 and converts volume of CH4 to mass of CH4. The density is taken at 20°C and 1 atmosphere pressure and has a value of 0.67 • 10-6 Gg m-3.

For the Tier 1 approach, it is good practice to use the low end of the specific emission range for those mines with average overburden depths of less than 25 meters and the high end for overburden depths over 50 meters. For intermediate depths, average values for the emission factors may be used. In the absence of data on overburden thickness, it is good practice to use the average emission factor, namely 1.2 m3/tonne.

The Tier 2 method uses the same equation as for Tier 1, but with data disaggregated to the coal basin level. POST-MINING EMISSIONS - SURFACE MINING

For a Tier 1 approach the post-mining emissions can be estimated using the emission factors shown in Equation 4.1.8.

Equation 4.1.8

Tier 1: global average method - post-mining emissions - surface mines

Methane emissions = CH4 Emission Factor • Surface Coal Production • Conversion Factor

Where units are:

Methane Emissions (Gg year-1) CH4 Emission Factor (m3 tonne-1) Surface Coal Production (tonne year-1) Emission Factor:

Low CH4 Emission Factor = 0 m3 tonne-1

Average CH4 Emission Factor = 0.1 m3 tonne-1

High CH4 Emission Factor = 0.2 m3 tonne-1

Conversion Factor:

This is the density of CH4 and converts volume of CH4 to mass of CH4. The density is taken at 20°C and 1 atmosphere pressure and has a value of 0.67 • 10-6 Gg m-3.

The average emission factor should be used unless there is country-specific evidence to support use of the low or high emission factor.