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| Titel |
Emissions and Distribution of Reactive Iodine from Seaweed in Coastal Regions |
| VerfasserIn |
Martin Horbanski, Denis Pöhler, Stefan Schmitt, Karin Kreher, Paul Johnston, Ulrich Platt |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250128706
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| Publikation (Nr.) |
 EGU/EGU2016-8718.pdf |
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| Zusammenfassung |
| Emissions and Distribution of Reactive Iodine from Seaweed in Coastal Regions Reactive
iodine species impact atmospheric chemistry in several ways. They play an important role in
the process of ozone destruction at mid-latitudes and possibly in polar regions. Besides
bromine, reactive iodine compounds also affect the atmospheric cleaning mechanisms by
changing its oxidation capacity. Recent field studies indicate that reactive iodine may impact
the local climate in coastal areas by playing a key role in the formation of new particles which
could influence cloud micro physical properties. Particularly high concentrations of the
reactive iodine are found at mid-latitude coastal sites, which are emitted by seaweed
exposed to oxidative stress during low tide. However, previous measurements of
iodine and iodine oxide have been performed only at very few sites, mainly at the
atmospheric research station Mace Head located at the west coast of Ireland. Thus,
there is still very limited knowledge on the involved seaweed species and their
contribution to local, regional and global iodine emissions and also the potential iodine
mediated particle formation. In order to investigate these questions, we performed
extensive measurements at ten different sites along the west coast of Ireland in
2011 and 2012. We applied a mobile Long Path (LP)-DOAS for path averaged IO
measurements and open path Cavity Enhanced (CE-) DOAS for IO in-situ measurements.
Similar to LP-DOAS, open path CE-DOAS measures trace gases directly in the
atmosphere. Additionally, another Long Path-DOAS system monitoring IO, OIO and
I2, was permanently located at Mace Head. This allows an inter-comparison of
the different locations with the reference station Mace Head while respecting the
influence of temporally varying meteorology. We observed significant differences to
former investigations and conclusions. First, IO concentrations were much higher
(typically factor of 10 and more) on every measuring site compared to Mace Head. IO
levels up to 40 ppt were observed with LP-DOAS and 70 ppt at 1.3 m height with
CE-DOAS. Second, we found out that Laminaria digitata is not a dominant iodine
source to the atmosphere, while Ascophyllum nodosum due to its high abundance in
the intertidal zone is by far the strongest source. Third, we observed also high IO
levels above 30 ppt at rainy, cold and windy weather. Thus former observations that
these emissions arise only at sunny and warm weather could not be confirmed.
Fourth, we investigated that IO increases rapidly with decreasing distance to the
emitting seaweed patches. Above the seaweed patches IO reaches concentrations much
above 50 ppt which is sufficient to start particle nucleation events. We conclude
that coastal seaweed emissions are thus much more relevant for the atmosphere
than so far expected from previous observations performed at Mace Head which is
rather characterized by low IO levels in comparison to other locations. Reasons and
explanations for these findings will be presented. A review of the coastal seaweed iodine
emissions and its influence on the atmosphere is thus urgently needed. In a third
field study on the east coast of the New Zealand south island, for the first time
high IO mixing ratios of up to 68 ppt were observed on a southern hemispheric
coast. Four, previously uninvestigated, seaweed species were identified as emitters
of reactive iodine species and emission rates were estimated. The observations
in New Zealand showed also differences in the seaweed distribution to northern
hemispheric locations which need to be considered in global estimates of coastal iodine
emissions. |
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