Geology Reference
In-Depth Information
at Mace Head in Ireland.
47
The data in Figure 23 show not only a
clear requirement for radiation for photochemical production of IO
but also a strong correlation with low tide conditions. The correlation
with low tidal conditions is indicative of the likely sources of IO, in
that the photolysis of organoiodine compounds (reaction (2.79)) such
as CH
2
I
2
and CH
2
IBr emitted from macroalgae in the intertidal zone
are possibly the candidate iodine sources. The photolysis lifetime of a
molecule such as diodomethane is only a few minutes at midday.
Recent experimental observations have suggested the I
2
can be emit-
ted directly from the macroalgae at low tide making this a substantial
source of iodine.
48
The chemistry can also lead to an enrichment of
iodine in the aerosol in the form of iodate providing a route to move
biogenic iodine from ocean to land.
47
Figure 23
[IO], tidal height and solar radiation measured at Mace Head in Ireland. The
grey areas represent the low-tide areas during the day. The dotted line in the
upper panel is the IO detection limit
46,47
