Quantification of methane oxidation measuring isotopic signal in 13C on Spanish landfills

Abstract

Landfill emissions, particularly methane leaks detected by satellite, are drawing great attention in the last years as a mean for evaluate their contribution to the global warming effect. In contrast, models like IPCC often overestimate landfill methane emissions, prompting verification and mitigation system evaluation. Methane's higher warming capacity than carbon dioxide underscores the importance of promoting its oxidation as it traverses landfill layers. This oxidation raises the CH₄–¹³C/¹²C ratio via bacterial biooxidation. This study quantified this fractionation using soil and surface gas samples from Spanish landfills and their degassing systems. Sampling relied on walkover surveys collecting samples in Tedlar bags, to analyze isotopic signals in the laboratory using WS-CRDS. Fractionation factors (α) ranged from 1.020 to 1.030, while the oxidized fraction (f_ox) spanned from no oxidation to 55% (δ¹³C of −45.83‰). Each ratio correlates with emission types like fugitive and dispersed emissions on plateaus, berms, slopes, sealing cracks, or pits. Understanding the methane oxidized fraction in each landfill is relevant for greenhouse gas emission model integration.