Methane record at Plateau Rosa confirms its role as background station with episodic sensitivity to European emissions

Methane mole fractions have been continuously measured since 2018 at Plateau Rosa, a background station in the north-western Italian Alps at 3480 m a.m.s.l., showing a persistent increase in methane over time. Here, we use the methane record to validate the high-resolution transport model FLEXPART coupled with the output of the numerical weather prediction model COSMO for complex alpine terrain and to identify European source regions affecting measurements at the stations. Comparison between simulated methane mole fraction contributions and observed increments indicate that summer advection of methane-rich air masses was not fully captured by the model, and most pollution events were underestimated in magnitude. The Po Valley, just below the Alps and with major urban and industrial activities, is the region affecting most pollution events, mainly from agriculture, while contributions from fuel exploitation increased when air originated from Germany, Poland, Czechia, the Netherlands, and the UK. Atmospheric transport models coupled with methane fluxes underestimate methane pollution events in the Alpine region, according to analysis of continuous methane measurements from the Plateau Rosa observatory in the Italian Alps.