Volcanogenic halocarbons

Previous investigations reported on the volcanic production of halocarbons including chlorofluorocarbons (CFCs). It has been suggested that this natur al source could account for a significant atmospheric CFC background concen tration, but no quantitative assessment of its source strength has yet been presented. The synthetic mechanism for their volcanic formation has neithe r been clarified. Fumarole and lava gas samples from four volcanoes (Kuju, Satsuma Iwojima, Mt. Etna, Vulcano) have been studied using gas chromatogra phy/ion trap-mass spectrometry. More than 300 organic substances were detec ted, among which 5 fluorinated, 100 chlorinated, 25 brominated, and 4 iodin ated compounds have been identified. The most abundant organohalogen specie s were chlorinated methanes, unsaturated C-2-chlorohydrocarbons, and chloro benzene, suggesting a synthetic course that includes the thermolytic format ion of acetylene from hydrothermal methane, condensation reactions, and syn chronous catalytic halogenation in the presence of highly activated surface s 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 pp bv. A conservative estimate of the upper limit of global CFC emissions by v olcanoes clearly shows that this source is negligible as compared to the at mospheric burden by anthropogenic activities.