Sulfur Species in Volcanic Gases

Abstract

A new analytical method for the determination of the sulfur species (SO2, H2S, S8(0)) in volcanic gases is proposed by revising, updating, and improving previous methods. The most significant advantages of the proposed procedure can briefly be summarized, as follows: (i) the reaction among sulfur species stops during the gas sampling by using preevacuated thorion-tapped vials with purified 0.15M Cd(OH)2 in 4 M NaOH to favor the precipitation of H2S as CdS; (ii) all the sulfur species (SO2, H2S, S8(0)) are analyzed by ion chromatography, after conversion to SO4, which allows the detection limit to be lowered significantly with respect to the previous studies; (iii) appropriate aliquots from intermediate steps may be used to determine other species commonly present in volcanic gases such as CO2, HCI, HF, HBr, HI, and so forth; (iv) determination of all the other gas species is not jeopardized by the proposed method, i.e., one single vial can be used for analyzing the full chemical composition of a volcanic gas with the exception of NH3. Statistical parameters calculated from gas sampling data at the F5 crater fumarole in Vulcano Island (Aeolian Islands, southern Italy), suggest that the standard error of mean (s/ root n) is higher for S (0.10), followed by SO2, H2S, and CO2 (0.04, 0.038, and 0.028, respectively). SO2 shows the higher variation coefficient (12.1%) followed by H2S, S, and CO2 (5.7, 1.5, and 0.8%, respectively). Furthermore, if the time dependence of sampling is taken into account, the measured values, instead of fluctuating in a random manner, tend to follow systematic patterns, out of statistical control, possibly suggesting a sort of natural fluctuation of the volcanic system. Other crater fumaroles from volcanic systems located in different geodynamical areas (Hawaii, USA, El Chichon, Mexico, Poas, Costa Rica) have been analyzed as well.

Geothermal potential and origin of natural thermal fluids in the northern Lake Abaya area, Main Ethiopian Rift, East Africa

“…Bubbling gases were sampled using an inverted plastic funnel, submerged in the pools, and Tygon® tube connections. Both fumaroles and bubbling gases were collected in pre-evacuated 60-mL glass Thorion®-tapped flasks filled with 20 mL of a 4 N NaOH and 0.15 M Cd(OH) 2 suspension (Montegrossi et al, 2001;Vaselli et al, 2006). During sampling, water vapour and acidic gas species (CO 2 , SO 2 , HCl and HF) dissolve in the alkaline solutions, H 2 S forms insoluble CdS, whereas low-solubility species (N 2 , O 2 , CO, H 2 , He, Ar, CH 4 and hydrocarbons) are stored in the flask headspace and concentrate in proportion to the quantity of solubilised acidic components in the NaOH.…”

Geochemistry of fluid discharges from Peteroa volcano (Argentina-Chile) in 2010–2015: Insights into compositional changes related to the fluid source region(s)

“…A plastic funnel upside-down submerged in the pools and connected to the sampling flasks through tygon tubes was used to sample the bubbling gases. Sampling flasks used to collect gases from both the discharges of the volcano summit and the bubbling pools consisted of pre-evacuated 60-mL glass thorion-tapped flask filled with 20 mL of 4 N NaOH and 0.15 M Cd(OH) 2 suspension (Montegrossi et al, 2001). During sampling, water vapor and acidic gas species (CO 2 , SO 2 , HCl and HF) dissolved in the alkaline solution, whereas H 2 S formed insoluble CdS.…”

“…Low-solubility gas species (N 2 , O 2 , CO, H 2 , He, Ar, Ne, CH 4 and light hydrocarbons) were concentrated in the sampling flask headspace. Aliquots of vapor condensates (for the analysis of δ 18 O and δD in water vapor) and dry gases (for the analysis of CO and 13 C/ 12 C ratio in CO 2 ) were sampled using an ice-cooled glass tube connected to the gas sampling line (Montegrossi et al, 2001;Vaselli et al, 2006). In 2012, six gas samples were collected in 100 mL sampling flasks filled with 50 mL of 4 N NaOH for the analysis of δ 15 N.…”

“…Argon and O 2 were analyzed using a Thermo Focus gas chromatograph equipped with a 30 m long capillary molecular sieve column and a TCD. A Shimadzu 14A gas chromatograph (GC) equipped with a 10-m-long stainless steel column packed with Chromosorb PAW 80/100 mesh coated with 23% SP 1700 and a flame ionization detector (FID (Montegrossi et al, 2001). HF concentrations were calculated on the basis of F − concentrations in the condensates.…”

The Geothermal Resource in the Guanacaste Region (Costa Rica): New Hints From the Geochemistry of Naturally Discharging Fluids

“…According to this indication, in 1999, two exploratory wells, PGT-1 and PGT-2, were drilled down to 2,473 m and 1,345 m depth, respectively (Mayorga, 2009). Unfortunately, the low temperature of the discharged water (<160 • C), the low permeability and the proximity of a protected area (Tenorio Volcano National Park) discouraged the development of geothermal exploitation (Mayorga, 2009) Gases from fumaroles were collected using a sampling line consisting of a 1 m-long titanium tube (Ø = 2.5 cm) and pyrex glass dewared pipes connected to pre-weighted and preevacuated 50-mL glass Thorion R -tapped flasks filled with 20 mL of a 4N NaOH and 0.15M Cd(OH) 2 suspension (Montegrossi et al, 2001). Bubbling gases were sampled using a funnel up-sidedown positioned above the bubbles and connected to the soda flasks using a silicon tube.…”