Physical properties of iodate solutions and the deliquescence of crystalline I2O5 and HIO3
Atmospheric Chemistry and Physics
Secondary aerosol produced from marine biogenic sources in algal-rich coastal locations will initially be composed of iodine oxide species, most likely I 2 O 5 , or its hydrated form HIO 3 , 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 (HIO 3 and I 2 O 5 share a common aqueous phase). With increased interest in the role of such aerosol in the marine atmosphere, we
... ne atmosphere, we have conducted studies of (i) the deliquescence behaviour of crystalline HIO 3 and I 2 O 5 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 solutions. The deliquescence of I 2 O 5 crystals at 293 K was observed to occur at a relative humidity (DRH) of 80.8±1.0%, whereas for HIO 3 , a DRH of 85.0±1.0% was measured. These values are consistent with measured water activity values for saturated I 2 O 5 and HIO 3 solutions at 293 K of 0.80±0.01 and 0.84±0.01 respectively. At all temperatures, DRH values for HIO 3 crystals were observed to be higher than for those of I 2 O 5 . The temperature-dependent DRH data, along with solubility and water activity data were used to evaluate the enthalpy of solution ( H sol ) for HIO 3 and I 2 O 5 . A H sol value of 8.3±0.7 kJ mol −1 was determined for HIO 3 which is consistent with a literature value of 8.8 kJ mol −1 . For I 2 O 5 , we report for the first time its solubility at various temperatures and H sol = 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.