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Atmos. Chem. Phys., 13, 5255-5264, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research Article
27 May 2013
The seaweeds Fucus vesiculosus and Ascophyllum nodosum are significant contributors to coastal iodine emissions
R.-J. Huang1,2,*, U. R. Thorenz1, M. Kundel1, D. S. Venables3, D. Ceburnis2, K. F. Ho5, J. Chen3, A. L. Vogel1, F. C. Küpper4, P. P. A. Smyth2, U. Nitschke6, D. B. Stengel6, H. Berresheim2, C. D. O'Dowd2, and T. Hoffmann1
1Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg University of Mainz, Duesbergweg 10–14, 55128 Mainz, Germany
2School of Physics and Centre for Climate and Air Pollution Studies, Ryan Institute, National University of Ireland Galway, University Road, Galway, Ireland
3Department of Chemistry and Environmental Research Institute, University College Cork, Cork, Ireland
4Oceanlab, University of Aberdeen, Main Street, Newburgh AB41 6AA, Scotland, UK
5School of Public Health and Primary Care, The Chinese University of Hong Kong, Shatin, Hong Kong, China
6Botany and Plant Science, School of Natural Sciences and Ryan Institute, National University of Ireland Galway, University Road, Galway, Ireland
*now at: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland

Abstract. Based on the results of a pilot study in 2007, which found high mixing ratios of molecular iodine (I2) above the intertidal macroalgae (seaweed) beds at Mweenish Bay (Ireland), we extended the study to nine different locations in the vicinity of Mace Head Atmospheric Research Station on the west coast of Ireland during a field campaign in 2009. The mean values of \chem{I_2} mixing ratio found above the macroalgae beds at nine different locations ranged from 104 to 393 ppt, implying a high source strength of I2. Such mixing ratios are sufficient to result in photochemically driven coastal new-particle formation events. Mixing ratios above the Ascophyllum nodosum and Fucus vesiculosus beds increased with exposure time: after 6 h exposure to ambient air the mixing ratios were one order of magnitude higher than those initially present. This contrasts with the emission characteristics of Laminaria digitata, where most I2 was emitted within the first half hour of exposure. Discrete in situ measurements (offline) of I2 emission from ambient air-exposed chamber experiments of L. digitata, A. nodosum and F. vesiculosus substantially supported the field observations. Further online and time-resolved measurements of the I2 emission from O3-exposed macroalgal experiments in a chamber confirmed the distinct I2 emission characteristics of A. nodosum and F. vesiculosus compared to those of L. digitata. The emission rates of A. nodosum and F. vesiculosus were comparable to or even higher than L. digitata after the initial exposure period of ~20–30 min. We suggest that A. nodosum and F. vesiculosus may provide an important source of photolabile iodine in the coastal boundary layer and that their impact on photochemistry and coastal new-particle formation should be reevaluated in light of their longer exposure at low tide and their widespread distribution.

Citation: Huang, R.-J., Thorenz, U. R., Kundel, M., Venables, D. S., Ceburnis, D., Ho, K. F., Chen, J., Vogel, A. L., Küpper, F. C., Smyth, P. P. A., Nitschke, U., Stengel, D. B., Berresheim, H., O'Dowd, C. D., and Hoffmann, T.: The seaweeds Fucus vesiculosus and Ascophyllum nodosum are significant contributors to coastal iodine emissions, Atmos. Chem. Phys., 13, 5255-5264, doi:10.5194/acp-13-5255-2013, 2013.
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