Evaluating the impact of anaerobic digesters on point source methane emissions from California dairies from remote sensing

Abstract Dairies are the largest source of methane (CH 4 ) emissions in California, with 57% of statewide emissions attributed to wet manure management systems. California has implemented CH 4 mitigation strategies, including anaerobic digesters (ADs), to capture and convert CH 4 produced by wet manure storage into renewable energy. While ADs are estimated to achieve large reductions in manure CH 4 emissions, studies centered on their performance and the potential for fugitive emissions remain limited. Here, we analyze CH 4 point source emissions at 98 California dairies from 2016 to 2024 using airborne imaging spectroscopy, covering pre-, during-, and post-digester installation periods. Emissions were attributed to housing, lagoons, digesters, and gas handling infrastructure. Overall emissions decreased significantly following installation from 91 ± 9–68 ± 9 kg CH 4 h −1 ( p = 0.001), with 68% of dairies exhibiting net reductions. However, digesters became the dominant emission source post-installation (47% of plumes), with some leaks exceeding 1000 kg CH 4 h −1 . Average emissions spiked during construction (197 ± 26 kg CH 4 h −1 ), significantly exceeding both pre- and post-installation levels. Lagoon persistence as emission sources decreased substantially after installation (from 72% to 24% of plumes), yet they remained significant contributors with broad emission ranges (60–675 kg CH 4 h −1 ). These findings demonstrate that remote sensing can successfully identify leaks from digesters and emphasizes the importance of frequent monitoring as a key strategy to improve digester efficiency. Comprehensive quantification of whole-farm emission reductions requires coordinated ground-based measurements and point source imaging.