Research Communications Volcanogenic Halocarbons A R M I N J O R D A N , * ,† J O C H E N H A R N I S C H , †,‡ REINHARD BORCHERS,† FRANCOIS LE GUERN,§ AND HIROSHI SHINOHARA| Max-Planck-Institute for Aeronomy, 37191 Katlenburg-Lindau, Germany, Laboratoire des Sciences du Climat et de l’Environnement, CNRS, Batiment 9, Avenue de la Terrasse, 91190 Gif sur Yvette, France, and Mineral and Fuel Resources Department, Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, 305-8567 Japan
Previous investigations reported on the volcanic production of halocarbons including chlorofluorocarbons (CFCs). It has been suggested that this natural source could account for a significant atmospheric CFC background concentration, but no quantitative assessment of its source strength has yet been presented. The synthetic mechanism for their volcanic formation has neither been clarified. Fumarole and lava gas samples from four volcanoes (Kuju, Satsuma Iwojima, Mt. Etna, Vulcano) have been studied using gas chromatography/ion trap-mass spectrometry. More than 300 organic substances were detected, among which 5 fluorinated, 100 chlorinated, 25 brominated, and 4 iodinated compounds have been identified. The most abundant organohalogen species were chlorinated methanes, unsaturated C2-chlorohydrocarbons, and chlorobenzene, suggesting a synthetic course that includes the thermolytic formation of acetylene from hydrothermal methane, condensation reactions, and synchronous catalytic halogenation in the presence of highly activated surfaces of cooling magma or juvenile ash. The only CFC compound found was CFCl3 (CFC-11), which was detected in some samples at concentrations of up to 1 ppbv. A conservative estimate of the upper limit of global CFC emissions by volcanoes clearly shows that this source is negligible as compared to the atmospheric burden by anthropogenic activities.
Introduction The driving role of chlorofluorocarbons (CFCs) in the depletion of stratospheric ozone is generally accepted (1). CFCs are commonly esteemed as purely anthropogenic. However, previous investigations (2-4) reported on the volcanic production of halocarbons including CFCs. It has been suggested that 75% of the world’s active volcanoes emit CFCs leading to a significant natural background concentration (3-5), but no quantitative assessment of the source * Corresponding author present address: Max-Planck-Institute for Biogeochemistry, Postfach 100164, 07701 Jena, Germany. Phone: ++49-3641-643815; fax: ++49-3641-643710; e-mail:
[email protected]. † Max-Planck-Institute for Aeronomy. ‡ Present address: ECOFYS Energy and Environment, Eupener Strasse 137, 50933 Cologne, Germany. § CNRS. | Geological Survey of Japan. 1122
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strength of these volcanic CFC emissions has yet been presented. The mechanism of their volcanic formation has been a matter of dispute (6, 7) as thermodynamic equilibrium calculations disfavor the presence of organic and haloorganic compounds in volcanic gases (7, 8). However, an increasing number of studies give evidence of the existence of hydrocarbons in volcanic gases (e.g., refs 2-4, 9, and 10), and a first approach to describe the synthetic processes for higher organic molecules formed in fumaroles from hydrothermal methane has been made (10). In this study, gas emanations from four volcanoes in Japan (Kuju and Satsuma Iwojima) and Italy (Mt. Etna and Vulcano) have been studied, and numerous halogenated trace gases have been identified. For the first time, lava gas samples from residual degassing on a lava flow (30 m from the main magmatic degassing crater) were analyzed for organohalogens, and the results give valuable information about the formation processes. A major aim of this study was to derive an upper limit for the global budget of natural emissions of CFCs based on measured data.
Experimental Section Gas samples are taken in 100-mL glass bottles, similar to those used by Giggenbach (11), which are sealed with a PTFE stopcock. The bottles were cleaned prior to usage by washing them with distilled water, drying, and evacuation to 10-5 mbar. They were then filled with purified synthetic air and re-evacuated twice. GC-MS analysis of this synthetic air did not show any halogenated compounds. Sampling is performed by pushing a silica tube into the fumarole or lava and inserting another tube with slightly smaller diameter. After the tubes were flushed with volcanic gas, an evacuated glass bottle is connected with an PTFEcoated O-ring to the inner tube, and the sample is sucked in. For analysis, sample volumes of 20 mL are pumped through an trap filled with an alkaline absorber (Ascarite) and then passed through a 0.7-mL stainless steel preconcentration loop filled with glass beads at liquid nitrogen temperature (-196 °C). After the permanent gases were pumped away, the sample loop was heated to 80 °C, and its contents were transferred to a small diameter unpacked focusing loop at -196 °C. The sample was then injected into the GC by rapidly heating the second loop and was analyzed in GC/ion trap-MS. Gas chromatographic separation was carried out on a DB1 column (60 m × 0.32 mm, film thickness 1 µm) using the following temperature program: initial oven temperature -65 °C, increasing rate 8 °C min-1 to 175 °C, 5 min isothermal. Mass spectrometric detection was performed over a scan range of 48-200 amu, and quantification was made using the most abundant fragment ion. Calibration was performed by a three-step static dilution procedure of the reference substances, except for chloroethyne. For an approximative quantification of this compound, the same instrumental response as for chloroethene was assumed. The replicate analysis of individual samples gave values within 10%.
Results and Discussion More than 300 organic substances were detected in fumarolic and lava gases, among which 5 fluorinated, 100 chlorinated, 25 brominated, and 4 iodinated compounds have been identified (Table 1). The greatest variety of halocarbons was found in the lava gas from the SE crater of Mt. Etna. Previously only 18 different volcanogenic organohalogens were known 10.1021/es990838q CCC: $19.00
2000 American Chemical Society Published on Web 02/04/2000
TABLE 1. Organohalogenated Compounds Detected in Fumaroles and Lava Gasa fluoro compds
chloro compds
fluorotrichloromethane trifluoropropene fluorobenzene tetrafluorobenzene fluorochlorobenzene
a
chloromethane dichloromethane trichloromethane tetrachloromethane fluorotrichloromethane chlorobromomethane dichlorobromomethane trichlorobromomethane chlorodibromomethane chloroiodomethane chloroethane dichloroethane (2) chlorobromoethane chloroethene dichloroethene (3) trichloroethene tetrachloroethene chlorobromoethene dichlorobromoethene (2) trichlorobromoethene chloroethyne dichloroethyne chloropropane chloropropene (4) dichloropropene (3) trichloropropene (2) tetrachloropropene (2) chlorobromopropene (3) dichlorobromopropene chloropropyne dichloropropyne (2) trichloropropyne tetrachloropropyne tetrachloropropadiene chlorobromopropyne dichlorobromopropyne
chlorobutane (4) dichlorobutane trichlorobutane tetrachlorobutane chlorobutene dichlorobutene (2) trichlorobutene chlorobromobutene chlorobutadiene (2) dichlorobutadiene (2) chlorobutenyne (2) dichlorobutenyne trichlorobutenyne chlorobutyne dichlorobutyne (2) tetrachlorobutadiene chlorocyclopentene (3) dichlorocyclopentene (2) trichlorocyclopentene chlorohexane chlorocyclohexane (2) chlorobenzene fluorochlorobenzene dichlorobenzene (3) trichlorobenzene (2) chlorotoluene (3) chloroethylbenzene chlorostyrene (3)
bromo compds
iodo compds
bromomethane dibromomethane tribromomethane chlorobromomethane dichlorobromomethane trichlorobromomethane chlorodibromomethane bromoethyne bromoethene bromoethane chlorobromoethane chlorobromoethene dichlorobromoethene (2) trichlorobromoethen bromopropene (3) chlorobromopropene (3) dichlorobromopene chlorobromopropyne dichlorobromopropyne bromobutane bromobutadiene chlorobromobutene bromobutyne bromobenzene bromofurane (2)
iodomethane chloroiodomethane iodoethane iodomethane
chlorofurane (2) dichlorofurane (2) chlorothiopene (2) dichlorothiophene (3) trichlorothiophene chloroselenophene (3)
The number of isomers is given in parentheses. Compounds containing two different halogens are listed in each of the respective columns.
TABLE 2. Concentrations of Halocarbons in Anhydrous Volcanic Gas (ppbv) volcano location date sample type temp (°C) sample no.
Etna SE crater NE crater 20MAR98 20MAR98 19MAR98 01OCT97 lava gas fumaroles fumaroles fumarole 1030 82/105 126/250 300 n)7 n)5 n)6 n)1
CH3Cl CH2Cl2 CHCl3 CCl4 CH3Br CH3I
0.95-74 0.04-12 0.05-3.7 0.04-6.1 0.16-3.7 0.11-1.4
10-18 0.09-1.8 1.8-5.5 2.9-9.2 0.50-1.5 0.07-0.62
0.61-1.2 0.01-0.08 0.03-0.12 0.10-0.25 0.01-0.04 0.02-0.13
CHtCCla CH2dCHCl CHCldCCl2 CCl2dCCl2
0.01-50 0.04-15 0.02-1.8 0.01-0.16
0.1-6 0.19-0.68 0.66-2.2 0.29-1.5
C6H5Cl CF2Cl2 CFCl3
0.06-30 0.11-0.28 0.03-0.09
3.4-5.3 0.21-0.41 0.16-0.28
a
Vulcano crater 22MAR98 fumaroles 99/235 n)2
84 0.49 0.42 0.23 1.4 1.9
