Evaluation of a Decade of Methane Observations From a Tower Network in Indianapolis, Indiana

Methane (CH 4 ) is a critical near‐term climate mitigation target, yet urban sources remain poorly constrained. Indianapolis hosts one of the world's longest and densest urban CH 4 data sets, with continuous measurements from a tall‐tower network spanning more than a decade. We leverage this record in a Bayesian inversion framework to quantify citywide CH 4 emissions for 2014–2023, evaluate temporal variability, and reconcile estimates with prior inventories and independent campaigns. Emissions from the South Side Landfill (SSLF), the city's largest point source, are estimated separately using a novel statistical approach applied to sorted tower enhancements. Across the decade, total Indianapolis CH 4 emissions averaged 2,900–3,700 kg , of which 1,370–1,760 kg originated from the SSLF. Emissions exhibited remarkable temporal stability, with annual variations within 14% of the mean. Seasonal differences were modest: winter emissions were 13% higher than summer, smaller than seasonal swings reported for other U.S. cities. Total emissions agree with aircraft mass‐balance estimates and an independently developed bottom‐up inventory but are difficult to compare with EPA inventory values because of conflicting emission estimates from two different landfill reporting methodologies in addition to large discrepancies in diffuse citywide emissions. This work finds diffuse emissions likely arise from leaks in the natural‐gas distribution system and equal 1.6%–2.4% of city consumption, despite leak‐tight plastic infrastructure, suggesting a predominantly post‐meter origin. These results demonstrate that long‐term, high‐density tower observations robustly quantify total and source‐specific urban CH 4 emissions, helping reconcile top‐down and bottom‐up estimates and inform effective mitigation strategies.