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

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.