Seasonal and Diurnal Dynamics of Atmospheric Radon, Carbon Dioxide, Methane, δ13C-CO2 and δ13C-CH4 in a Proposed Australian Coal Seam Gas Field

Abstract

The expected growth of the coal seam gas industry in Australia requires baseline information for determining any potential long-term impacts of the industry. As such, a 1-year atmospheric time series measuring radon (222Rn), methane (CH4), carbon dioxide (CO2), δ13C-CO2 and δ13C-CH4 was conducted in an area where coal seam gas (CSG; also referred to as coal bed methane) extraction is proposed (Casino, New South Wales, Australia). We hypothesise that 222Rn can be used as a tracer of soil-atmosphere CH4 and CO2 exchange, and that carbon stable isotope values of atmospheric CH4 and CO2 can be used to identify the source of greenhouse gases. Radon, CO2 and CH4 followed a diurnal pattern related to increased concentrations during the formation of a nighttime inversion layer. The study found a significant inverse linear relationship between 222Rn concentrations and both rainfall (r 2∈=∈0.43, p∈