First estimation of CH4 fluxes using the 222Rn tracer method over the central Iberian Peninsula

Emissions of CH₄ over the central Iberian Peninsula have been estimated experimentally for the first time using the Radon Tracer Method (RTM), which uses the atmospheric noble radioactive gas 222Rn as an auxiliary tracer. The nocturnal enhancement ratios of atmospheric concentrations of CH₄ and 222Rn, continuously measured at the station of Gredos and Iruelas within the IC₃ network since 2012, were used to early estimate the methane emissions in this region by multiplying for a constant radon flux. The possible influence of different methane source areas was observed by footprint analysis of FLEXPART with ECMWF meteorological input at 0.2 degrees horizontal resolution. A linear relationship between atmospheric radon and methane concentrations has been found to occur in 20% of the nocturnal episodes and an average methane emission of 0.12 mg m-2 h-1 ± 0.03 (1 σ). The data coverage and method is coherent with CH₄ fluxes inferred with the same RTM in Germany, Canada and East Asia and our flux estimates are similar to methane emissions reported by the bottom-up inventory EDGARv4.2.