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.