Methane variability associated with natural and anthropogenic sources in an Australian context

ABSTRACT

Coal seam gas (CSG) has the potential to be a low-carbon transition fuel, but CSG fields may be a source of fugitive emissions of methane (CH₄). We use mobile cavity ring-down spectroscopy (CRDS) measurements to attribute CH₄ concentrations to sources in southeastern Australia including CSG fields. Our study shows higher CH₄ concentration values associated with both natural and anthropogenic sources other than CSG. These include urban landfills (>320 ppm) and urban infrastructure (>17 ppm), agricultural activities (>20 ppm) and open-pit coal mines (>30 ppm). We confirm reports of increased concentration of CH₄ downwind of some parts of CSG fields (<5 ppm), but elevated concentrations are not endemic and could not be separated from contributions of natural geological seeps (>16 ppm) that form part of the background levels. While CRDS allows direct determination of CH₄ sources, repeat measurements show the strong influence of atmospheric conditions on concentration and highlight the need for methods that quantify flux.

KEYWORDS:

• methane concentration
• coal seam gas
• spatial variability
• temporal variability
• fugitive emissions

Acknowledgments

We thank Grant Edwards for his helpful comments on earlier drafts of the manuscript. The assistance of M. Barnes and B. Clark in obtaining the data is gratefully acknowledged. Geoscience Australia and CSIRO are thanked for their assistance in the calibration of our CRDS.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Financial support for this work was provided by the Environment Institute of The University of Adelaide, the Department of State Development of the Government of South Australia, Santos Pty Ltd, and the Australian Research Council [grant number LP140100460] and [grant number LP120200086].