Intercomparing CO 2 amounts from dispersion modeling, 1.6 µm differential absorption lidar and open path FTIR at a natural CO 2 release at Caldara di Manziana, Italy

Abstract

We intercompare results of three independent approaches to quantify a vented CO 2 re-lease at a strongly non-uniform CO 2 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 CO 2 concentrations in parallel at 5 two different paths. An Eulerian gas dispersion model simulated 3-D CO 2 concentra-tion maps in the same area, using in situ CO 2 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 CO 2 concentrations in the instrument measurement paths. The model, on the other hand, also considers atmospheric effects that are out of the 10 field of view of the instruments. Despite this we find satisfactory agreement between modeled and measured CO 2 concentrations under certain meteorological conditions. Under these conditions the results suggest that an Eulerian dispersion model and opti-cal remote sensing can be used as an integrated, complementary monitoring approach for CO 2 hazard or leakage assessment. Furthermore, the modeling may assist in evalu-15 ating CO 2 sensing surveys in the future. CO 2 column amounts from differential absorp-tion 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 CO 2 emissions, including volcanoes.