Volcanic eruptions inject substantial amounts of halogens into the
atmosphere. Chlorine and bromine oxides have frequently been observed in
volcanic plumes from different instrumental platforms such as from ground, aircraft
and satellites. The present study is the first observational
evidence that iodine oxides are also emitted into the atmosphere during
volcanic eruptions. Large column amounts of iodine monoxide, IO, are observed
in satellite measurements following the major eruption of the Kasatochi
volcano, Alaska, in 2008. The IO signal is detected in measurements made both
by SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY) on
ENVISAT (Environmental Satellite) and GOME-2
(Global Ozone Monitoring Experiment-2) on MetOp-A (Meteorological Operational Satellite A).
Following the eruption on
7 August 2008, strongly elevated levels of IO slant columns of more than
4 × 1013 molec cm−2 are retrieved along the volcanic plume
trajectories for several days. The retrieved IO columns from the different
instruments are consistent, and the spatial distribution of the IO plume is
similar to that of bromine monoxide, BrO. Details in the spatial
distribution, however, differ between IO, BrO and sulfur dioxide,
SO2. The column amounts of IO are approximately 1 order of
magnitude smaller than those of BrO. Using the GOME-2A observations, the
total mass of IO in the volcanic plume injected into the atmosphere from the
eruption of Kasatochi on 7 August 2008, is determined to be on the order of
10 Mg