Nocturnal Trapping of Agricultural Emissions Drives Persistent Methane Enhancements at the Southern Great Plains

Abstract Long‐term atmospheric monitoring sites provide the observations used to evaluate greenhouse‐gas inventories and constrain atmospheric inversions. The Southern Great Plains (SGP) observatory, among the most heavily utilized sites in the U.S. Department of Energy Atmospheric Radiation Measurement program, has exhibited persistently elevated methane (CH 4 ) that existing bottom‐up inventories cannot explain. Combining multi‐year tower observations (2011–2024) with a mobile campaign (June 2024), we trace these CH 4 enhancements to a large animal feeding operation 5.8 km from the site. Mass‐balance estimates yield emission rates of 59–79 kg hr −1 , exceeding the EDGAR v8.0 agricultural CH 4 for the surrounding 0.1° grid cell (∼4 kg hr −1 ) by more than an order of magnitude. Strongly stable nocturnal boundary layers recurrently trap these emissions near the surface, producing CH 4 enhancements exceeding 300 ppb within the lowest 25 m. These findings demonstrate that underestimated point sources, amplified by boundary‐layer trapping, can dominate signals at sites relied upon for inventory validation. Regional inversions that assimilate such local records without resolving the underlying source may systematically overestimate the emissions in the surrounding area.