CO 2 flux measurements in volcanic areas using the dynamic concentration method: Influence of soil permeability

In order to evaluate the influence of soil permeability on soil CO 2 flux measurements performed with the dynamic concentration method, several tests were carried out using soils characterized by different permeability values and flow rates. A special device was assembled in the laboratory to create a one‐dimensional gas flow through a soil of known permeability. Using the advective‐diffusion theory, a physical model to predict soil concentration gradients was also developed. The calculated values of CO 2 concentrations at different depths were compared with those measured during the tests and a good agreement was found. Four soils with different gas permeability (3.6 × 10 −2 to 1.23 × 10 2 μm 2 ) were used. The CO 2 flux values were varied from 0.1 kg m −2 d −1 up to 22 kg m −2 d −1 . On the basis of these results, a new empirical equation for calculating very accurate soil CO 2 flux from dynamic concentration and soil permeability values was proposed. As highlighted by the experimental data, the influence of soil permeability on CO 2 flux measurements depends on various factors, of which the flow rate of the suction pump is the most important. Setting low values for the pumping flux (0.4–0.8 L min −1 ), the mean error due to soil permeability was lower than 5%. Finally, the method was tested by measuring the CO 2 flux in a grid of 48 sampling sites on Vulcano (Aeolian Islands, Italy), and the global error, affecting the CO 2 flux measurements in a real application, was evaluated.