Continuous gas sampling and analysis at the Pisciarelli fumarolic field (Campi Flegrei) by using a quadrupole mass spectrometer (QMS)

Abstract

Volcanic monitoring has as main goal the identification of typical phenomena of impending-eruption precursors. Therefore, recording a large amount of data of volcanic gases composition, during the quiescence period, is fundamental in order to identify baseline values to be distinguished from any anomalous geochemical signal. The gases emitted by most of the volcanoes are difficult to be sampled especially when the volcano is restless. Volcanic gases have traditionally been monitored by means of direct in situ sampling of fumaroles, followed by laboratory analysis [e.g., Symonds et al., 1994]. However, since direct sampling is often impractical and hazardous, particularly during eruptions, or of too low temporal resolution, efforts have been made (since the 1970s) to improve volcanological applications of optical remote sensing techniques [Pedone et al., 2014; and references therein]. Soil-gas surveys of hydrothermal volcanoes in a quiescent condition have also quantified diffuse CO2 emissions, but much less information has been obtained on fumarolic CO2 emissions. Because of these difficulties, the volcanic CO2 flux (the most reliable gas precursor to an eruption, [Aiuppa et al., 2015]) inventory remains sparse and incomplete for most of the active volcanoes on Earth [Burton et al., 2013]. Collection of fumarole gases is – depending on the state of volcanic activity, for logistics and other practical reasons – mostly performed discontinuously with time intervals ranging from days, weeks or even months between consecutive sample collections [Pecoraino and Giammanco, 2005]. Conventional sampling requires that operators collect fluid samples directly from the fumarolic vent in different kind of flasks directly on site. By this way any short-term variation in gasgeochemical parameters may be missed.