Using stable isotopes of hydrogen to quantify biogenic and thermogenic atmospheric methane sources: A case study from the Colorado Front Range

Global atmospheric concentrations of methane (CH₄), a powerful greenhouse gas, are increasing, but because there are many natural and anthropogenic sources of CH₄, it is difficult to assess which sources may be increasing in magnitude. Here we present a data set of δ²H-CH₄ measurements of individual sources and air in the Colorado Front Range, USA. We show that δ²H-CH₄, but not δ¹³C, signatures are consistent in air sampled downwind of landfills, cattle feedlots, and oil and gas wells in the region. Applying these source signatures to air in ground and aircraft samples indicates that at least 50% of CH₄ emitted in the region is biogenic, perhaps because regulatory restrictions on leaking oil and natural gas wells are helping to reduce this source of CH₄. Source apportionment tracers such as δ²H may help close the gap between CH₄ observations and inventories, which may underestimate biogenic as well as thermogenic sources.