Quantification of methane emission rates from coal mine ventilation shafts using airborne remote sensing data

[摘要] The quantification of emissions of the greenhouse gas methane is essentialfor attributing the roles of anthropogenic activity and natural phenomena inglobal climate change. Our current measurement systems and networks, whilsthaving improved during the last decades, are deficient in many respects. Forexample, the emissions from localised and point sources such as landfills orfossil fuel exploration sites are not readily assessed. A tool developed tobetter understand point sources of the greenhouse gases carbon dioxide andmethane is the optical remote sensing instrument MAMAP (Methane airborne MAPper), operated fromaircraft. After a recent instrument modification, retrievals of the column-averageddry air mole fractions for methane XCH₄ (or forcarbon dioxide XCO₂) derived from MAMAP data havea precision of about 0.4% or better and thus can be used to inferemission rate estimates using an optimal estimation inverse Gaussian plumemodel or a simple integral approach.

CH₄ emissions from two coal mine ventilation shafts in westernGermany surveyed during the AIRMETH 2011 measurement campaign are used asexamples to demonstrate and assess the value of MAMAP data for quantifyingCH₄ from point sources. While the knowledge of the wind is animportant input parameter in the retrieval of emissions from point sourcesand is generally extracted from models, additional information froma turbulence probe operated on-board the same aircraft was utilised toenhance the quality of the emission estimates. Although flight patterns wereoptimised for remote sensing measurements, data from an in situ analyser forCH₄ were found to be in good agreement with retrieved dry columns ofCH₄ from MAMAP and could be used to investigate and refine underlyingassumptions for the inversion procedures.

With respect to the total emissions of the mine at the time of theoverflight, the inferred emission rate of50.4 kt CH₄ yr⁻¹ has a difference of less than1% compared to officially reported values by the mine operators, whilethe uncertainty, which reflects variability of the sources and conditions aswell as random and systematic errors, is about ±13.5%.

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