Estimating regional methane emissions using the Radon Tracer Method – a case study from North Italy

Due to its relatively short half-life, radon (²²²Rn) is considered a tracer of boundary layer mixing processes. This property is exploited in the Radon Tracer Method (RTM), a top-down technique for estimating local-to-regional emissions of trace gases. However, its applicability has been shown to be site-specific and to require experimental measurement of soil radon exhalation. Here, we apply the RTM to estimate regional methane emissions in the footprint of the ICOS (Integrated Carbon Observation System) Ispra 100m tall tower in northern Italy.  We present methane and radon concentrations from the tall tower, alongside measurements of soil radon exhalation rate and soil water content conducted at two sites near the tower between 2023 and 2025. Methane fluxes are calculated using two types of radon flux as input to the RTM: 1) radon fluxes measured in situ, and 2) modeled radon fluxes obtained from the traceRadon project. We find that both approaches yield comparable methane flux estimates, supporting the use of modeled radon fluxes as an alternative to direct measurements. Furthermore, the resulting methane fluxes are in good agreement with anthropogenic emissions reported by the EDGAR inventory.