A review of landfill methane emission detection, localization, and quantification systems

We address the need for more accurate and effective monitoring of methane emissions from landfills by reviewing traditional and emerging emissions detection, localization, and quantification field-based technologies. This review explores the advantages and limitations of current and emerging technologies and defines each monitoring technology as a system composed of a platform, sensor hardware, and data post-processing. Mathematical models (e.g., Landfill Gas Emissions Model (LandGEM)) are briefly discussed but are not the focus of this review. We note that, among the current technologies used for landfill monitoring, some are widely accepted by regulators but are not necessarily well-proven scientifically to be accurate and reliable methods for monitoring landfill methane emissions. We discuss the accuracy and coverage limitations of widely used and traditional approved methods such as manual walking surface emissions monitoring (SEM) and unmanned aerial vehicle (UAV) SEM. We note that mature technologies, such as mobile tracer correlation and aircraft-based flux measurements, provide reliable estimates of emissions rates but lack leak localization, and mobile vehicle-based measurements provide accurate emission estimates at relatively lower cost. Advanced technologies like aerial imaging and Light Detection and Ranging (LiDAR) offer quantification and localization despite unresolved uncertainties. Emerging technologies, including UAV flux plane and UAV column methods, satellite imaging, and remote point fixed sensors, have strong potential for cost-effective and scalable deployment, though many still require methodological improvements to improve their emission quantification accuracy. Any of the quantification technologies discussed in this review can be used to provide a snapshot of the methane emissions from a landfill. However, it should be remembered that none of the technologies can provide a robust annual inventory from a single measurement. A robust annual inventory requires repeated measurements over time and a combination of complementary technologies to capture all emission sources.