Environmental Engineering Reference
In-Depth Information
(4) A series of day- and nighttime observations at Masaya volcano, Nicaragua
using active DOAS (Kern
et al
.,
2009
) revealed that BrO levels signi
cantly
exceed zero only during daytime (see
Fig. 8.5b
). This observation con
rms
that BrO formation in volcanic plumes is a photochemical process.
(5) Measurements of the BrO/SO
2
ratios at Etna and Nevado del Ruiz volcanoes
during eruptive and non-eruptive periods show clearly that during eruptions
signi
cantly lower BrO/SO
2
ratios prevail than for non-eruptive periods
found a drop in the BrO/SO
2
ratio from
10
-5
preceding the
eruption on 30 June 2012 by about 5 months. After the eruption, the BrO/SO
2
ratio reverted to the initial level.
(6) There are indications that bromine might behave differently from chlorine and
10
-5
4
to
<
2
BrO/SO
2
data set and an empirical model, that bromine
-
in contrast to Cl and
F (see, e.g., Aiuppa,
2009
)
could be of low effective solubility in the melt
and thus could already be emitted by deep degassing magma (similar to CO
2
).
Further indications for this unexpected
-
finding are measurements at the Nyir-
agongo lava lake, which show simultaneous and correlated variations in the
CO
2
/SO
2
and BrO/SO
2
ratios. However, since BrO is largely a secondary
species, it has yet to be shown that the BrO/SO
2
ratio is directly correlated with
the Br/S ratio.
8.5 Summary
During the recent decade, modern spectroscopic technology and advanced
in situ
observations have given new insight into volcanic halogen emission and chemical
transformation processes in volcanic plumes. In particular, detailed analyses of the
temporal and spatial distribution of reactive halogen species in volcanic plumes
have revealed that complex multi-phase (photo-) chemistry is taking place there.
For instance hydrogen halides (HCl and HBr, probably also HI) can be transformed
into reactive halogen species.
Quantitative studies of volcanic emissions and plume chemistry make up a new
field, which is still in its infancy. While chemical equilibrium modelling is
relatively well developed, there are only a few studies of chemical reaction kinetics
in volcanic plumes. Among the many unknowns are the abundance of reactive
chlorine and iodine species and their temporal evolution (e.g. of the XO/SO
2
ratio)
in the plume.
Reactive halogen species can profoundly in
uence atmospheric chemistry on a
regional or even global scale. We are just beginning to understand the in
uences of
volcanic halogens on the budgets of ozone and other oxidants, their contribution to
