Forward Modeling and Optimization of Methane Emissions in the South Central United States Using Aircraft Transects Across Frontal Boundaries

Abstract

The South Central United States is a hot spot for anthropogenic methane (CH4) emissions, with contributions from the oil/gas (O&G) and animal agriculture sectors. During frontal weather events, airflow combines enhancements from these emissions into a large plume. In this study, we take CH4 and ethane (C2H6) observations from the Atmospheric Carbon and Transport‐America campaign and adjust O&G and animal agriculture emissions such that modeled CH4 and C2H6 enhancements match the observed plume. Results from the joint CH4‐C2H6 optimization indicate that emissions from the O&G sector are 1.8 ± 0.7 (2σ) times larger than EPA inventory estimates. These results match synthesis work from recent literature and reject the possibility that this increase compared to inventories is due to a potential bias in daytime‐only measurements of these facilities. Successful modeling from this study raises the possibility of using trace gas measurements along frontal crossings to solve for emissions in other regions of the United States.

Aircraft-based inversions quantify the importance of wetlands and livestock for Upper Midwest methane emissions

“…Here, A (t, d) is wetland extent (m 2 wetland area/m 2 surface area) based on either GLOBCOVER (Bontemps et al, 2011) or the Global Lakes and Wetlands Database (GLWD) (Lehner and Döll, 2004), with temporal variability prescribed using satellite-based surface water or reanalysis-based precipitation datasets (Bloom et al, 2017); R (t, d) is heterotrophic respiration rate (mgC/d/m 2 of wetland area) taken as the median monthly value from the Carbon Data Model Framework (CARDAMOM; Bloom et al, 2016); T is surface skin temperature ( • C); q 10 quantifies the T dependence of methane emissions relative to heterotrophic C respiration (i.e. the CH 4 : C temperature dependence), with q 10 = 1, 2, or 3; and s is a scaling factor imposing a global flux of 124.5, 166, or 207.5 Tg CH 4 /yr (Saunois et al, 2016;Bloom et al, 2017).…”

Emergency deployment of direct air capture as a response to the climate crisis

“…We include fugitive methane emissions at 0.32% leakage rate, the collective 2017 average methane intensity of aggregated upstream gas and oil operations of Oil and Gas Climate Initiative members—the firms that have most conspicuously embedded methane control into their operations and are targeting cuts to 0.25% by 2025. Although the impact of fugitive methane emissions is small in our analysis—a direct result of our assumption of leakage rate—the problem is serious 41 – 43 . We expect that a crisis response leading to massive deployment of DAC would strictly enforce best practices for producing and transporting methane that might be needed to power the technology.…”

Quantifying Nitrous Oxide Emissions in the U.S. Midwest: A Top‐Down Study Using High Resolution Airborne In‐Situ Observations

“…We adopted the method of Barkley et al. (2019a) to assess uncertainties in our solutions. F AGR is affected by uncertainties in the following variables: observed background mole fraction A nonAGR A N model transport model wind speed and PBL height (PBLH) spatial distribution in EDGAR emissions …”

“…By combining these observations with forward model simulations, we optimize agricultural fluxes from EDGAR version 4.3.2 and version 5.0 to quantify Midwest N 2 O emissions. The employed method was already successfully applied in several methane top‐down studies (Barkley et al., 2017, 2019a, 2019b). The derived emission rates are finally compared to flux estimates of direct soil emissions produced with EDGAR and the biogeochemical model DayCent (Del Grosso et al., 2001, 2011; Parton et al., 1998).…”