Direct methane measurements in a coal mine ventilation shaft: instrument intercomparison and emission estimates

Abstract. Methane released through coal mine ventilation shafts is a major source of anthropogenic greenhouse gas emissions. Reliable quantification of ventilation air methane (VAM) is increasingly important for emission reporting and mitigation, yet long-term in-situ datasets remain scarce. This study presents one year of continuous methane measurements obtained in an exhaust ventilation shaft of an underground hard coal mine in the Upper Silesian Coal Basin (Poland). High-resolution measurements from a tunable diode laser absorption spectroscopy (TDLAS) analyser were compared with data from the mine’s routine monitoring system based on catalytic pellistor sensors. Methane concentrations varied between 0.15 and 0.45 % CH₄ and exhibited pronounced diurnal, weekly, and seasonal variability primarily associated with mining activity. The pellistor sensor reproduced long-term concentration trends but systematically underestimated methane levels. Following recalibration against the TDLAS measurements, agreement improved substantially (R² = 0.93), demonstrating that corrected pellistor datasets can support quantitative CH₄ assessments. Methane emission rates were derived from combined concentration and airflow measurements and ranged from 0.8 to 1.7 t CH₄·h⁻¹. Total annual methane emissions from the monitored ventilation shaft were estimated at 10.7 ± 0.93 kt CH₄·yr⁻¹. Emission variability closely followed changes in mining activity and showed stronger relationships with longwall advance than with coal production alone. The resulting methane emission factor was 5.1 ± 1.0 m³ CH₄·t⁻¹ coal, while a geometrical emission factor of 13.4 ± 2.4 m³ CH₄·m⁻² of longwall advance was identified. These results demonstrate the value of continuous high-resolution monitoring for improving methane emission quantification, evaluating routine mine monitoring systems, and supporting measurement-based approaches to mine-level methane reporting.