Diffuse and Visible Emission of CO2 from Etna Volcano, Italy

Abstract

This work reports the first estimation of total CO2 emission to the atmosphere (visible and non-visible) from Etna volcano, Sicily, by means of direct methods. Until present, only direct measurements of the CO2 emitted by the volcanic plume of Etna had been performed, and not data of direct soil CO2 efflux from surface environment of this volcano were available. To estimate the total CO2 emission, 4075 soil CO2 efflux measurements were performed by means of the accumulation chamber method in October-November 2008. Most of the study area showed background levels of soil CO2 efflux (0.53 g·m-2·d-1), while peak values (>1725 g·m-2·d-1) were mainly identified inside the summit craters and at Torre del Filosofo area. Other zones with relatively high CO2 efflux values were identified at Paternó, Zafferana Etnea and Trecastagni-Viagrande. The total output of CO2 diffuse emission from the study area (973 km2) was computed in 20320 t·d-1, where 1671 t·d-1, about 8.3% of CO2 diffuse emission, was emitted by an area of 87 km2 which includes the summit craters and Torre del Filosofo. To evaluate the visible/diffuse CO2 emission ratio, plume CO2 emission rate was estimated by multiplying SO2 emission rate times observed CO2/SO2 plume ratio following the methodology described by Shinohara (2005). Total CO2 visible emission was estimated about 31.5 kt·d-1, value is in the range reported for Etna volcano (0.9-67.5 kt·d-1; Aiuppa et al., 2006). The total output of CO2 diffuse emission represents 39% of the total CO2 emission from Etna volcano to the atmosphere. These results agree with the observations of Allard et al. (1991), who reported that diffuse and visible CO2 emissions were in the same order of magnitude. This study demonstrates the importance of measuring diffuse CO2 emissions from active volcanoes like Mt. Etna in order to have a better approach on the global estimate of CO2 emission to the atmosphere from subaerial volcanoes