Source partitioning of atmospheric methane using stable carbon isotope measurements in the Reuss Valley, Switzerland

Measurements of methane ( $$ ) mole fractions and $$ $$ that resolve the diel cycle in the agriculturally dominated Reuss Valley, Switzerland, were used to quantify the contributions of different $$ sources to the atmospheric $$ source mix. Both a nocturnal (NBL) and a diurnal convective boundary layer (CBL) approach were employed. A diel course of $$ mole fractions was found with a daytime minimum (background around 1900 ppb) and a nocturnal maximum (up to 3500 ppb). The $$ C value in $$ only showed small variations during the day (9-21 hours CET, $$ ‰ $$ ) when the atmosphere was well mixed, but decreased by $$ ‰ during the night. Biogenic emissions dominated in both approaches (ranging from 60 to 94%), but non-biogenic sources were rather important (42.2% and 46.0% with CBL, 5.8% and 40% with NBL approach in 2011 and 2012, respectively, of total emissions). The $$ sink, dominated by tropospheric OH oxidation and only to a minor extend by soil surface uptake, was quantified at roughly 4% of local emissions.