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. Plain Language Summary Despite the large number of oil and gas wells in the Denver region, our analyses indicate that cattle, which are also present in very large numbers, landfills, wastewater treatment, and/or natural biological sources are the dominant source of methane in the region. Key Points Biogenic and thermogenic CH4 have distinct hydrogen isotopic ratios in Colorado Hydrogen isotopes indicate that biogenic sources comprise at least 50% of CH4 in the Front Range Potential for resolving differences between methane inventories and observations regionally and globally