Expanding the tracer correlation method (TCM): A performance-based framework for wider implementation in landfill...

The Tracer Correlation Method (TCM), when applied to quantify landfill methane emissions, relies on previously developed stringent quality control thresholds (R² ≥ 0.80 and Emission Rate Deviation (ERD) ≤ 20 %, hereafter referred to as the Gold Standard. However, these thresholds often exclude a substantial portion of the collected data, limiting wider use of TCM. We evaluated TCM during a controlled release campaign at the Petrolia landfill (Ontario, Canada), where methane was emitted at known rates (27.1-179 kg/h), though these were not disclosed to the measurement team during testing. Emission estimates from the TCM (slope-based and area-based) were compared to the true releases using the Symmetric Mean Absolute Percentage Error (SMAPE). While transects fulfilling the Gold Standard threshold showed strong agreement with actual emissions, several non-Gold Standard transects also yielded emissions estimates within 20-30 % of the released rates. These results were used to propose an expanded classification framework introducing a Silver category (R² ≥ 0.60, ERD ≤ 30 %), that retained additional valid transects under moderate conditions. These results demonstrate that TCM can provide accurate total landfill emission estimates supporting a more flexible, performance-based framework to improve its utility in landfill monitoring programs.