Measurements of δ¹³C in CH₄ and using particle dispersion modeling to characterize sources of arctic methane within an air mass

A stratified air mass enriched in methane (CH₄) was sampled at ~600m to ~2000m altitude, between the north coast of Norway and Svalbard as part of the Methane in the Arctic: Measurements and Modelling campaign on board the UK’s BAe-146-301 Atmospheric Research Aircraft. The approach used here, which combines interpretation of multiple tracers with transport modeling, enables better understanding of the emission sources that contribute to the background mixing ratios of CH₄ in the Arctic. Importantly, it allows constraints to be placed on the location and isotopic bulk signature of the emission source(s). Measurements of δ¹³C in CH₄ in whole air samples taken while traversing the air mass identified that the source(s) had a strongly depleted bulk δ¹³C CH₄ isotopic signature of -70 (±2.1)%. Combined Numerical Atmospheric-dispersion Modeling Environment and inventory analysis indicates that the air mass was recently in the planetary boundary layer over northwest Russia and the Barents Sea, with the likely dominant source of methane being from wetlands in that region.