Abstract
Different types of laboratory experiments were carried out during this study. In type A experiments a standard gas mixture is continuously injected, at constant flux, into the accumulation chamber, mimicking the soil CO 2 flux measurements performed in field surveys. In type B experiments, a standard gas mixture is initially injected into the accumulation chamber for a short lapse of time, to achieve a relatively high CO 2 concentration inside the accumulation chamber; then the injection of the standard gas mixture is stopped and the CO 2 concentration inside the chamber is monitored for a sufficient interval of time. In both types of experiments, the accumulation chamber appears to be flushed by a considerable flux of atmospheric air, which is virtually constant in each experiment but is different from experiment to experiment. The occurrence of this air flux through the accumulation chamber (i) has no effect on the determination of the soil CO 2 flux on the basis of the initial slope (at time zero) of the CO 2 concentration-time curve, but (ii) it complicates the evaluation of the two components of the soil CO 2 flux, namely the CO 2 molar fraction of soil gas and the flux of the soil gas mixture. A method to obtain both the CO 2 molar fraction of soil gas and the flux of the soil gas mixture is presented and the implications related to the knowledge of the two components of the soil CO 2 flux are discussed.
Highlights
Most of these FCO2 studies have been performed adopting the accumulation chamber method, where an inverted chamber is positioned on the ground, the CO2 concentration inside the chamber is monitored, and the initial slope of the CO2 concentration-time curve is used to compute the FCO2 [Chiodini et al, 1998]
From the CO2 time series acquired by means of the accumulation chamber method, and (3) the implications related to the knowledge of the two components of FCO2, in order to underscore why it is important to know FCO2 and FG and XCO2,G
The form of the drawdown curve, with decrease of CO2 concentration with time and negative slope decreasing with time, indicates that the accumulation chamber is continuously flushed by atmospheric air
Summary
Since the early 1990’s, the soil CO2 flux, FCO2, has been measured, mapped, and monitored at sites worldwide for geothermal exploration, volcanic surveillance, surface monitoring of CO2 geological sequestration sites and other geo-scientific purposes [e.g., Baubron et al, 1990 1991; Allard et al, 1991; Chiodini et al, 1996, 1998, 2001, 2007, 2008; Hernández et al, 1998, 2001; Carapezza and Federico, 2000; Lewicki and Brantley, 2000; Werner et al, 2000; Bergfeld et al, 2001; Brombach et al, 2001; Salazar et al, 2001; Carapezza and Granieri, 2004; Frondini et al, 2004, 2009; Notsu et al, 2005; Fridriksson et al, 2006; Werner and Cardellini, 2006; Padrón et al, 2008a; Carapezza et al, 2009; Evans et al 2009; Toutain et al, 2009; Mazot et al., 2011; Rissmann et al, 2012; Parks et al, 2013; Dionis et al, 2015; Hutchison et al, 2015; Jolie et al, 2015; Lee et al, 2016; Robertson et al, 2016]. These uncertainties can be mitigated by imposing known FCO2 values and calibrating the system [Chiodini et al, 1998]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
