Atmos. Chem. Phys. Discuss., 12, 7879-7908, 2012
www.atmos-chem-phys-discuss.net/12/7879/2012/
doi:10.5194/acpd-12-7879-2012
© Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Glass formation and unusual hygroscopic growth of iodic acid solution droplets with relevance for iodine oxide particles in the coastal marine boundary layer
B. J. Murray1, A. E. Haddrell2, S. Peppe1, J. F. Davies2, J. P. Reid2, D. O'Sullivan1, H. C. Price1, R. Kumar1,3, R. W. Saunders3, J. M. C. Plane3, N. S. Umo1, and T. W. Wilson1,3
1School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
2School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK
3School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK

Abstract. Iodine oxide particles are known to nucleate in the marine boundary layer where gas phase molecular iodine and organoiodine species are produced by macroalgae. There has been some debate over the chemical identity of these particles. Hygroscopic measurements have been used to infer that they are composed of insoluble I2O4, while elemental analysis of laboratory generated particles suggests soluble I2O5 or its hydrated form iodic acid, HIO3 (I2O5 · H2O). In this paper we explore the response of super-micron sized aqueous iodic acid solution droplets to varying humidity using both Raman microscopy and single particle electrodynamic traps. These measurements reveal that the propensity of an iodic acid solution droplet to crystallise is negligible on drying to ~0% relative humidity (RH). On applying mechanical pressure to these droplets they shatter in a manner consistent with an ultra-viscous liquid or a brittle glass, but subsequent water uptake between 10 and 20% RH causes their viscosity to reduce sufficiently that the cracked droplets flow and merge. The persistence of iodic acid solution in an amorphous state, rather than a crystalline state, suggests they will more readily accommodate other condensable material and are therefore more likely to grow to sizes where they may serve as cloud condensation nuclei. On increasing the humidity to ~90% the mass of the droplets only increases by ~20% with a corresponding increase in radius of only ~6 %, which is remarkably small for a highly soluble material. We suggest that the small growth factor of aqueous iodic acid solution droplets is consistent with the small aerosol growth factors observed in field experiments.

Citation: Murray, B. J., Haddrell, A. E., Peppe, S., Davies, J. F., Reid, J. P., O'Sullivan, D., Price, H. C., Kumar, R., Saunders, R. W., Plane, J. M. C., Umo, N. S., and Wilson, T. W.: Glass formation and unusual hygroscopic growth of iodic acid solution droplets with relevance for iodine oxide particles in the coastal marine boundary layer, Atmos. Chem. Phys. Discuss., 12, 7879-7908, doi:10.5194/acpd-12-7879-2012, 2012.
 
Search ACPD
Discussion Paper
    XML
    Citation
    Final Revised Paper
    Share