Accurate identification of the early stages of coal-fire combustion is important for effectively controlling the spread of coal fires. CO2 and CO, as characteristic gases in the early stage of coal fire combustion, can be effectively monitored by in-situ monitoring near the surface. However, in the previous in-situ monitoring methods, the influence of surface meteorological and soil factors on the release law of characteristic gases is often ignored. Therefore, this paper considers the complexity of the geological conditions in the coal fire area, a system, and equipment for obtaining the near-surface CO2 and CO variation laws in the early stage of coal fire combustion proposed by the concentration gradient method (CGM). The system and equipment realize the simultaneous online coupling of multi-area and multi-parameter data and conduct field investigations on the Wuda coal fire area. The results show that in the early stage of coal combustion, the change patterns of CO2 and CO concentrations in different regions are anomalous, and the CO2 concentration was higher than the CO concentration. The CO2 and CO concentrations in shallow soil increased with the increase of soil depth, and compared with other areas, the CO2 and CO concentration was the highest. The shallow soil and CO2 were identified as the key areas and characteristic gases for identifying the early stage of coal-fire combustion. The CO2 flux (CF) of different shallow soil depths decreased with increased soil layer depth. Variation of soil-surface CO2 flux (S-SCF) estimated by flux extrapolation method (FLEM). The change of S-SCF is controlled by meteorological and soil factors, and there is a certain connection between it and the "respiration phenomenon" in the fissure area. Thus, this study provides a theoretical basis for effectively identifying the early stages of coal-fire combustion.
Keywords: CO(2) flux; Early stages of coal fire combustion; Fissure area; Shallow soil; Surface layer.
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