Fig. 5. Comparison of concentration of CO₂ in the soil determined from the porous Teflon tubing, closed-loop design to CO₂ concentrations from samples extracted from the in-line air stream of the closed-loop design and gas wells buried at 0.02, 0.1, and 0.18 m below the soil surface. Root mean square (rms) = [( predicted values – measured values)²/number of data]^0.5.