Modelling Iodine Particle Formation and Growth from Seaweed in a Chamber

L. Pirjola; C. D. O’Dowd; Y. J. Yoon; K. Sellegri

doi:10.1071/EN05075

RESEARCH FRONT

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Modelling Iodine Particle Formation and Growth from Seaweed in a Chamber

L. Pirjola ^A ^E , C. D. O’Dowd ^B , Y. J. Yoon ^B ^C and K. Sellegri ^B ^D

+ Author Affiliations

- Author Affiliations

^A Helsinki Polytechnic, Department of Technology, Helsinki, Finland and University of Helsinki, Department of Physical Sciences, Helsinki, Finland.

^B Department of Experimental Physics and Environmental Change Institute, National University of Ireland, Galway, Ireland.

^C Korea Polar Research Institute/KORDI/Ansan P.O. Box 29, Seoul 425-600 Korea.

^D Univesité Blaise Pascal, Laboratoire de Météorologie Physique, Clermont-Ferrand, France.

^E Corresponding author. Email: liisa.pirjola@stadia.fi

Environmental Chemistry 2(4) 271-281 https://doi.org/10.1071/EN05075
Submitted: 21 September 2005 Accepted: 21 October 2005 Published: 8 December 2005

Environmental Context. Iodine is an important trace species in the marine atmosphere. It contributes to ozone depletion and new particle formation. In recent years, its importance has been realised, however, there is still a gap in our knowledge, from a theoretical framework, of the dominant mechanisms leading to new particle formation and previous theoretical frameworks have not been adequately developed or well understood. This paper presents a state-of-the-art theoretical framework for evaluating the prediction of iodine oxide nucleation and subsequent aerosol growth.

Abstract. A sectional atmospheric chemistry and aerosol dynamics box model (AEROFOR) was further developed and used to simulate ultra-fine particle formation and growth from seaweed in a chamber flushed with particle-free atmospheric air. In the model, thermodynamically stable clusters were formed by dimer nucleation of OIO vapour, whose precursor was assumed to be molecular I₂ emitted by seaweed. Fractal geometry of particles was taken into account. For the I₂ fluxes of (0.5–1.5) × 10⁹ cm⁻³ s⁻¹ the model predicted strong particle bursts, the steady state concentrations of I₂ vapour and particles larger than 3 nm were as high as 4 × 10⁹–1.2 × 10¹⁰ cm⁻³ and 5.0 × 10⁶–9.2 × 10⁶ cm⁻³ respectively. The steady state was reached in less than 150 s and the predicted growth rates of 3–6 nm particles varied in the range of 1.2–3.6 nm min⁻¹. Sensitivity of the size distribution against I₂O₃ cluster formation, an extra condensable vapour, the photolysis rate of the OIO vapour as well as against the density of (OIO)_n-clusters was discussed. The modelled results were in good agreement with the chamber measurements performed during the BIOFLUX campaign in September, 2003, in Mace Head, Ireland, confirming that I₂ emissions and nucleation of iodine oxides can largely explain the coastal nucleation phenomenon.

Keywords. : aerosol dynamics — growth rate — iodine chemistry — modelling — natural emissions

Acknowledgments

The authors acknowledge for Science and Engineering Technology (IRCSET) and European Commission under contract EVK-CT-2001-00127 (QUEST). Special thanks go to Gordon McFiggans for helpful discussions.

References

Modelling Iodine Particle Formation and Growth from Seaweed in a Chamber

Acknowledgments

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