Diffuse emission of organic trace gases from the flank and crater of a quiescent active volcano (Vulcano, Aeolian Islands, Italy)

Abstract

[1] Volcanoes discharge a range of inorganic major gas species (e.g., H 2 O, CO 2 , SO 2 , and CO) not only during eruptions but also during quiescent phases through fumarolic and diffuse degassing in their craters and on their flanks. The emission of organic trace gases from volcanoes is similarly not expected to be restricted to discrete fumarolic gas discharges alone. To test this hypothesis, we have sampled soil gas emissions for organic compounds and determined CO 2 fluxes along a profile extending from the vegetated base of the active La Fossa cone (Vulcano Island, Italy) over the unvegetated volcanic flank and up into the crater rim and base and then continuing over fumarolic areas. The results indicate that the majority of volatile organic compounds in the soil gas show significant increases in concentration toward the crater and fumaroles and that diffuse emissions contribute significantly to the volcanic halocarbon source strength. Emissions of the halocarbon CFC-11 (CCl 3 F) correlate well with soil CO 2 fluxes measured on site (R 2 = 0.89, slope = 1.42 ± 0.1) and both increase toward the crater and fumaroles. Other ozone-depleting substances were found in concentrations significantly above those found in field and system blanks, including CH 3 Br, CH 3 Cl, CH 3 I, C 2 H 5 Br, and chlorinated benzenes. Abundances ranged from upper pptv to ppmv; for example, the maximum observed CFC-11 concentrations were 1200 pptv in diffuse emissions and 3700 pptv in dry fumarolic gas (average dry air is 268 pptv). On the basis of these results the natural volcanic source strength of halocarbon emissions to the atmosphere requires reevaluation, and in some cases, correction to higher values. Global average fumarolic and diffuse halocarbon source strengths were estimated and scaled to known global volcanic fumarolic and diffuse CO 2 flux data. Among these were CFC-11 (8.56 ± 4.7 Â 10 À6 Tg y À1 ), CH 3 Br (0.98 ± 0.47 Â 10 À6 Tg y À1 ), CHCl 3 (94.9 ± 27.6 Â 10 À6 Tg y À1 ), and CCl 4 (3.41 ± 1.0 Â 10 À6 Tg y À1 ).

Sorbent Tube Sampling and an Automated Thermal Desorption System for Halocarbon Analysis

“…The con cen tra tions of CH 2 Cl 2 and CHCl 3 re corded were highly el e vated at all sites es pe cially the back ground area, which is for ested (mainly lodgepole pine trees) in di cat ing that the vol cano could be a po ten tial source of them. Pre vious stud ies (Isidorov et al 1990;Schwandner et al 2004) de tected higher CH 2 Cl 2 and CHCl 3 con cen tra tions in the vol ca nic gas sam ples. Schwandner et al (2004) sug gested that the in creased CH 2 Cl 2 con cen tra tions in the vol ca nic gas were as so ci ated with el e vated ground resistivities in dicat ing a subsurface or i gin.…”

“…Pre vious stud ies (Isidorov et al 1990;Schwandner et al 2004) de tected higher CH 2 Cl 2 and CHCl 3 con cen tra tions in the vol ca nic gas sam ples. Schwandner et al (2004) sug gested that the in creased CH 2 Cl 2 con cen tra tions in the vol ca nic gas were as so ci ated with el e vated ground resistivities in dicat ing a subsurface or i gin. These com pounds are also known to have ter res trial sources and these ob ser va tions are con sis tent with this.…”

“…Isidorov et al (1990) reported 0.4 -1.5 ppbv of CFCs in sol fa ta ric air and Jor dan et al (2000) de tected CFC-11 in gas sam ples of vol ca noes at con cen tra tions of up to 1 ppbv. Schwandner et al (2004) also ob served 1200 and 3700 pptv of CFC-11 in dif fuse emis sions from the ac tive vol cano and dry fumarolic gas, respectively. The cur rent study sug gests that the max i mum con cen tra tions of CFC-12 and CFC-11 in the Yel low stone vol cano sam ple are 1.3 and 1.7 times higher than background val ues.…”

“…In the Yel low stone cam paign, the re corded con cen tra tions of the CFC-11 and CFC-12 for Hot Hill and Gib bon Meadow were much higher than the ur ban background val ues and also back ground val ues from the AGAGE net work sug gest ing that vol ca nic emis sions could be a source of these CFCs. Pre vi ous stud ies (Isidorov et al 1990;Jor dan et al 2000;Schwandner et al 2004) re ported the emis sion of CFCs from vol ca noes. Isidorov et al (1990) reported 0.4 -1.5 ppbv of CFCs in sol fa ta ric air and Jor dan et al (2000) de tected CFC-11 in gas sam ples of vol ca noes at con cen tra tions of up to 1 ppbv.…”

Ecosystem responses to elevated CO<sub>2</sub> using airborne remote sensing at Mammoth Mountain, California

“…Hernández et al, 1998;Cardellini et al, 2003;Werner and Brantley, 2003;Giammanco et al, 2007;Lewicki et al, 2014a). Although the spatial distributions of CO2 emissions within tree kill areas have been well mapped (Pickles et al, 2001;Werner and Brantley, 2003;List et al, 2005, and others), linking CO2 measurements to vegetation 10 responses along a spatially diffuse CO2 degassing continuum is a natural yet underutilized opportunity for studying the effects of elevated CO2 on plants (Schwandner et al, 2004). Furthermore, many CO2 emissions in volcanic systems have been ongoing for decades or centuries, thus allowing for the observation of equilibrium, long-term ecosystem responses after transient and acclimational responses have passed.…”