Abstract
Abstract. Currently, the atmospheric methane burden is rising rapidly, but the extent to which shifts in coal production contribute to this rise is not known. Coalbed methane emissions into the atmosphere are poorly characterised, and this study provides representative δ13CCH4 signatures of methane emissions from specific coalfields. Integrated methane emissions from both underground and opencast coal mines in the UK, Australia and Poland were sampled and isotopically characterised. Progression in coal rank and secondary biogenic production of methane due to incursion of water are suggested as the processes affecting the isotopic composition of coal-derived methane. An averaged value of −65 ‰ has been assigned to bituminous coal exploited in open cast mines and of −55 ‰ in deep mines, whereas values of −40 and −30 ‰ can be allocated to anthracite opencast and deep mines respectively. However, the isotopic signatures that are included in global atmospheric modelling of coal emissions should be region- or nation-specific, as greater detail is needed, given the wide global variation in coal type.
Highlights
Methane emissions from the energy sector have been driven in recent years using the impact of a shift from coal to natural gas, in the US and Europe, whereas in China coal production has increased over this century
For the UN Framework Convention on Climate Change, national emissions are estimated by a bottom-up approach, based upon a general equation where the coal production data are multiplied by an emission factor that takes into account the mine’s gassiness, which in turn is related to the depth of the mine and the coal rank (US EPA, 2013)
Methane plumes from Hatfield colliery, one of the few British deep mines still open at the time of this study, were detected during surveys on 10 July and 26 September 2013
Summary
Methane emissions from the energy sector have been driven in recent years using the impact of a shift from coal to natural gas, in the US and Europe, whereas in China coal production has increased over this century. For the UN Framework Convention on Climate Change, national emissions are estimated by a bottom-up approach, based upon a general equation where the coal production data are multiplied by an emission factor that takes into account the mine’s gassiness, which in turn is related to the depth of the mine and the coal rank (i.e. carbon content of coal) (US EPA, 2013). These modelled estimates are often reported without an error assessment; the level of accuracy of the emissions is not known. This top-down approach provides the total amount of methane emissions into the atmosphere, which has to be distributed among the different methane sources in order to quantify each source contribution
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