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

Stieger, Jacqueline, Bamberger, Ines, Siegwolf, Rolf T. W., Buchmann, Nina, Eugster, Werner
Isotopes in environmental and health studies 2019 v.55 no.1 pp. 1-24
emissions, methane, oxidation, soil, stable isotopes, troposphere, 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.