Environmental Engineering Reference
In-Depth Information
Nearly all data on Br contents and Br/Cl ratios in volcanic emanations originate
from condensate samples collected at volcanic arcs (Gerlach,
2004
, and references
therein). Very little data exist on the Br inventory of explosive eruptions, and
most values are estimated from measured Cl concentrations using experimentally
determined Cl/Br ratios for fluids in magmatic systems (Bureau
et al
.,
2000
), or
using halogen ratios measured in fumaroles (Symonds
et al
.,
1994
; Gerlach,
2004
).
Each of the approaches may give ambiguous results, as both degassing processes
and reactions with surrounding rocks (in the case of fumarole gases) in
uence the
Cl/Br ratios. In order to achieve consistent petrologic data on released masses
of Br from large eruptions, re
ned analytical tools were developed using focused
synchrotron radiation (Hansteen
et al
.,
2000
). Using an optimized synchrotron
micro-X-ray
fluorescence (XRF) setup, detection limits for Br of about 0.5 ppm
in typical glass inclusions have been achieved, which enables the analyses of a
glass inclusion within minutes (Kutterolf
et al
.,
2013a
). A combination of electron
microprobe and synchrotron micro-XRF (for Br only) thus allows for semi-routine
measurements of S, Cl and Br in typical glass inclusions and glassy matrix
originating from Plinian eruptions. This method has so far been used to determine
the halogen inventory of 31 Quaternary eruptions in Central America, covering
an along-arc distance of 1200 km (Kutterolf
et al
.,
2013a
; unpublished).
16.3 Volcanic halogen entrainment into the present-day stratosphere
Emissions of Cl and Br play an important role for the catalytic destruction of ozone
in the present-day stratosphere. Most studies concentrate on the anthropogenic
release of these gases in the form of chloro
uorocarbons and their substitute
halons, which caused the ozone hole over Antarctica since the 1980s (Chubachi,
1984
; Farmann
et al
.,
1985
). More recently, the role of biogenic oceanic halogen
sources has been investigated for the stratospheric halogen and ozone loading,
revealing a small but not negligible role under the present-day high Cl loading
(Montzka
et al
.,
2011
, and references therein). However, the relevance of other
natural halogen sources such as from present-day large volcanic eruptions for the
stratospheric ozone layer has hardly been discussed in the past. This may be partly
due to the fact that the amount of halogens emitted from the respective volcanic
vent into the stratosphere is highly uncertain. Observations after the El Chichón
(1982) eruption revealed a 40% increase in total chloride column 3 to 6 months
after the eruption in the region of the volcanic cloud (Mankin and Coffey,
1984
),
while after the Pinatubo (1991) eruption no signi
cant increase in the HCl concen-
tration was detected (Mankin
et al
.,
1992
; Wallace and Livingston,
1992
). On the
other hand, investigation of both volcanogenic halogens Cl and Br together are
restricted to observations from the Plinian El Chichón 1982 eruption and relatively
