Atmospheric dispersion of volcanic CO2 at Vulcano island

Abstract

Intensive carbon dioxide emanations occur throughout the island of Vulcano (Aeolian Archipelago, north of Sicily, Italy). The main sources of CO2 on the island are the hot fumaroles (∼500°C) of the northern ridge of the La Fossa crater, the fumaroles of the Baia di Levante and the emission areas spread out both on the slopes of the cone and in the nearby plain. The carbon dioxide from the soil can be considered as being emitted at air temperature.In this work, CO2 concentrations in the air over the island are estimated by means of two numerical codes. This paper takes advantage of the parallel knowledge gained from a previously written paper for SO2 emissions from the La Fossa volcanic cone (J. Volcanol. Geotherm. Res., 75 (1997) 283). Here the attention is focused on CO2 and on the roles the different CO2 sources play in the inhabited area of Vulcano Porto village. In the model chain, the wind flow is simulated using a 3D mesoscale meteorological model for complex terrain. The simulations are performed for the most significant large-scale wind conditions derived from a meteorological analysis of the region. Flow model outputs are then used by way of a Lagrangian particle model to simulate the dispersion of the gas and to calculate the concentrations. The space and time evolution of gas concentration is discussed for various sources and output rates.Simulations show that the contributions to the concentrations at the inhabited area of Vulcano Porto village of: (1) the cone slopes and the La Forgia Vecchia emitting areas; and (2) of the crater fumaroles are both negligible. The main contribution comes from the soil emission at the volcano feet. Results agree well with field measurements, indicating a sharp decrease in CO2 concentration downwind, and nocturnal peaks of few hundred ppm in the areas emitting 10−3cm3(CO2 STP)/cm2s.The approach shows the absence of any risk to population at the present emission rates.