Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 4 2005 10.5194/acpd-5-5405-2005 http://www.atmos-chem-phys-discuss.net/5/5405/2005/ http://www.atmos-chem-phys-discuss.net/5/5405/2005/acpd-5-5405-2005.html http://www.atmos-chem-phys-discuss.net/5/5405/2005/acpd-5-5405-2005.pdf 5405 5439 2005-07-28 Modelling molecular iodine emissions in a coastal marine environment: the link to new particle formation A. Saiz-Lopez J. M. C. Plane G. McFiggans P. I. Williams S. M. Ball M. Bitter R. L. Jones C. Hongwei T. Hoffmann School of Environmental Sciences, University of East Anglia, Norwich, UK School of Earth, Atmospheric & Environmental Sciences, University of Manchester, Manchester, UK University Chemical Laboratory, Cambridge University, Cambridge, UK Institute of Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg-University, Mainz, Germany A model of iodine chemistry in the marine boundary layer (MBL) has been used to investigate the impact of daytime coastal emissions of molecular iodine (I₂). The model contains a full treatment of gas-phase iodine chemistry, combined with a description of the nucleation and growth, by condensation and coagulation, of iodine oxide nano-particles. In-situ measurements of coastal emissions of I₂ made by the broadband cavity ring-down spectroscopy (BBCRDS) and inductively coupled plasma-mass spectrometry (ICP/MS) techniques are presented and compared to long path differential optical absorption spectroscopy (DOAS) observations of I₂ at Mace Head, Ireland. Simultaneous measurements of enhanced I₂ emissions and particle bursts show that I₂ is almost certainly the main precursor of new particles at this coastal location. The ratio of IO to I₂ predicted by the model indicates that the iodine species observed by the DOAS are concentrated over a short distance (about 8% of the 4.2 km light path) consistent with the intertidal zone, bringing them into good agreement with the I₂ measurements made by the two in-situ techniques. The model is then used to investigate the effect of iodine emission on ozone depletion, and the production of new particles and their evolution to form stable cloud condensation nuclei (CCN).