QUANTIFYING ATMOSPHERIC CO₂ EMISSIONS FROM COAL FIRES: SAMPLING APPROACHES AND SOME U.S. EXAMPLES

Spontaneous coal fires occur in nearly all coal-producing parts of the world. The magnitude of coal fire emissions is poorly constrained and as such, coal-fires are generally not included as a source category in estimating global atmospheric greenhouse and toxic gas budgets. In an effort to begin to quantify the magnitude of coal-fire emissions, a ground-based approach was developed to calculate fluxes of CO₂ from several coal fires in the U.S. This approach combines CO₂ emissions from vent fluxes and diffuse soil fluxes. Vent fluxes are calculated from CO₂ concentrations, vent flow, and vent area measurements. Soil flux measurements are taken in a gridded pattern circumscribing the fire and interpolated using geostatistical methods. This combination of techniques was applied to active coal fires along the Tongue River in the Powder River Basin, Wyoming, including the Welch Ranch fire and the Hotchkiss fire. Comparison of calculated vent emissions with preliminary estimates of diffuse CO₂ soil flux indicates diffuse fluxes are similar to or less than vent emissions. For the Welch Ranch fire, vent emissions are 6.8 ± 2.4 Mg CO₂ d^-1. For the Hotchkiss fire, vent emissions are 0.65 ± 0.05 Mg CO₂ d^-1. For a third Powder River Basin Fire, the Ankney Fire, access and safety concerns limited measurement coverage so that a partial vent flux of 1.6 ± 0.3 Mg CO₂ d^-1 was determined. Vent measurements of CO, CH₄, H₂S and Hg allow calculation of vent emissions for these constituents from each fire. For the Welch Ranch fire, these values range from 270 ± 47 mg d^-1 for Hg to 18 ± 6.3 kg d^-1 for CO. Ground-based measurements for the three Powder River Basin coal fires are being compared to contemporaneous airborne tropospheric CO₂ measurements and thermal infrared imaging in order to integrate ground-based and airborne determinations.