Intercomparing CO₂ amounts from dispersion modeling, 1.6 μm differential absorption lidar and open path FTIR at a natural CO₂ release at Caldara di Manziana, Italy

Abstract. We intercompare results of three independent approaches to quantify a vented CO₂ release at a strongly non-uniform CO₂ Earth degassing at Caldara di Manziana, central Italy. An integrated path differential absorption lidar prototype and a commercial open path FTIR system were measuring column averaged CO₂ concentrations in parallel at two different paths. An Eulerian gas dispersion model simulated 3-D CO₂ concentration maps in the same area, using in situ CO₂ flux input data acquired at 152 different points. Local processes the model does not account for, such as small-scale and short-lived wind eddies, govern CO₂ concentrations in the instrument measurement paths. The model, on the other hand, also considers atmospheric effects that are out of the field of view of the instruments. Despite this we find satisfactory agreement between modeled and measured CO₂ concentrations under certain meteorological conditions. Under these conditions the results suggest that an Eulerian dispersion model and optical remote sensing can be used as an integrated, complementary monitoring approach for CO₂ hazard or leakage assessment. Furthermore, the modeling may assist in evaluating CO₂ sensing surveys in the future. CO₂ column amounts from differential absorption lidar are in line with those from FTIR for both paths with a mean residual of the time series of 44 and 34 ppm, respectively. This experiment is a fundamental step forward in the deployment of the differential absorption lidar prototype as a highly portable active remote sensing instrument probing vented CO₂ emissions, including volcanoes.