H. Bureau et al., Volcanic degassing of bromine and iodine: experimental fluid/melt partitioning data and applications to stratospheric chemistry, EARTH PLAN, 183(1-2), 2000, pp. 51-60
In order to understand the degassing behavior of heavy halogens in Volcanic
processes, we experimentally studied the distribution of Cl, Br, and I bet
ween albite melt and hydrous fluids containing 0.01-2 wt% of NaCl, NaBr, or
NaI, respectively. All experiments were carried out at 2 kbar and 900 degr
eesC in rapid-quench cold-seal autoclaves with a run duration of 7 days. Th
e major element compositions and CI contents of the glassy run products wer
e measured by electron microprobe. Bromine and iodine were measured by prot
on-induced X-ray emission. Fluid compositions were obtained by mass balance
. All halogens investigated were found to partition strongly into the fluid
phase. Over the range of concentrations studied, the halogen contents in t
he melt are proportional to the concentrations in the fluid. The fluid/melt
partition coefficients, D-f/m, are 8.1 +/- 0.2 for CI, 17.5 +/- 0.6 for Br
, and 104 +/- 7 for I. The logarithm of D-f/m is linearly correlated with t
he ionic radius of the halogenide ion. On the basis of our experimental dat
a, we estimate the amount of bromine injected into the stratosphere by majo
r volcanic explosions. For the 1991 Mount Pinatubo eruption, we obtain Br y
ields of 11-25 kt as minimum estimates. These numbers are comparable to the
total annual influx of bromine into the stratosphere from all other natura
l and anthropogenic sources (about 100 kt/year). Since bromine is much more
efficient in destroying stratospheric ozone than chlorine, it could at lea
st be partially responsible for the massive ozone depletion observed after
the 1991 Mount Pinatubo eruption. (C) 2000 Elsevier Science B.V. All rights
reserved.