Atmospheric dispersion of volcanic CO2 at Vulcano island

Intensive carbon dioxide emanations occur throughout the island of Vulcano (Aeolian Archipelago, north of Sicily, Italy). The main sources of CO2 on t he island are the hot fumaroles (similar to 500 degreesC) of the northern r idge of the La Fossa crater, the fumaroles of the Baia di Levante and the e mission areas spread out both on the slopes of the cone and in the nearby p lain. The carbon dioxide from the soil can be considered as being emitted a t air temperature. In this work, CO2 concentrations in the air over the island are estimated b y 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, th e wind flow is simulated using a 3D mesoscale meteorological model for comp lex terrain. The simulations are performed for the most significant large-s cale wind conditions derived from a meteorological analysis of the region. Flow model outputs are then used by way of a Lagrangian particle model to s imulate the dispersion of the gas and to calculate the concentrations. The space and time evolution of gas concentration is discussed for various sour ces and output rates. Simulations show that the contributions to the concentrations at the inhabi ted 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 negligibl e. 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 a reas emitting 10(-3) cm(3) (CO2 STP)/cm(2) s. The approach shows the absence of any risk to population at the present emi ssion rates. (C) 2001 Elsevier Science B.V. All rights reserved.