Physical properties of iodate solutions and the deliquescence of crystalline I2O5 and HIO3 1School of Chemistry, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
23 Dec 2010
*now at: Laboratory for Atmospheric and Climate Science (CIAC), CSIC, 45007 Toledo, Spain
**now at: School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
Received: 12 July 2010 – Published in Atmos. Chem. Phys. Discuss.: 01 September 2010 Abstract. Secondary aerosol produced from marine biogenic sources in algal-rich
coastal locations will initially be composed of iodine oxide species, most
likely I2O5, or its hydrated form HIO3, formed as a result of
iodine gas-phase chemistry. At present, there is no quantitative hygroscopic
data for these compounds and very little data available for iodate solutions
(HIO3 and I2O5 share a common aqueous phase). With increased
interest in the role of such aerosol in the marine atmosphere, we have
conducted studies of (i) the deliquescence behaviour of crystalline
HIO3 and I2O5 at 273–303 K, (ii) the efflorescence
behaviour of aqueous iodate solution droplets, and (iii) properties (water
activity, density, and viscosity) of subsaturated and saturated iodate
Revised: 03 December 2010 – Accepted: 15 December 2010 – Published: 23 December 2010
The deliquescence of I2O5 crystals at 293 K was observed to occur
at a relative humidity (DRH) of 80.8±1.0%, whereas for HIO3,
a DRH of 85.0±1.0% was measured. These values are consistent with
measured water activity values for saturated I2O5 and HIO3
solutions at 293 K of 0.80±0.01 and 0.84±0.01 respectively. At
all temperatures, DRH values for HIO3 crystals were observed to be
higher than for those of I2O5. The temperature-dependent DRH data,
along with solubility and water activity data were used to evaluate the
enthalpy of solution (ΔHsol) for HIO3 and I2O5.
A ΔHsol value of 8.3±0.7 kJ mol−1 was determined
for HIO3 which is consistent with a literature value of 8.8 kJ mol−1.
For I2O5, we report for the first time its solubility
at various temperatures and ΔHsol = 12.4±0.6 kJ mol−1.
The measured water activity values confirm that aqueous iodate
solutions are strongly non-ideal, consistent with previous reports of
complex ion formation and molecular aggregation.
Citation: Kumar, R., Saunders, R. W., Mahajan, A. S., Plane, J. M.C., and Murray, B. J.: Physical properties of iodate solutions and the deliquescence of crystalline I2O5 and HIO3, Atmos. Chem. Phys., 10, 12251-12260, doi:10.5194/acp-10-12251-2010, 2010.