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Title: Formation and properties of iodine oxide nano-particles in the atmosphere
Author: Kumar, Ravi
ISNI:       0000 0004 2747 9023
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2011
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The results from the laboratory experiments of iodine oxide particle (lOP) formation processes and properties are presented. The formation and growth of lOPs, originating from molecular iodine precursor, have been studied at 293 K as a function of water vapour and sulphuric and oxalic acids vapour. Under dry conditions, a linear variation in total lOP mass in particles was observed for a range of iodine concentrations. The observed hygroscopic growth factors of <1 at RH 10 - 90% on addition of H20 vapour to the particles formed under dry conditions are consistent with the particles having a fractal-like, aggregated structure. The uptake of sulphuric acid vapour onto humidified particles lead to condensational growth, with an accommodation coefficient (α) of 0.75 ± 0.05 at RH = 90% and a predicted growth rate of ~ 0.03 - 0.3 nm per hour with respect to marine boundary layer (MBl) conditions. In contrast, growth of particles exposed to oxalic acid vapour was not observed on the experimental timescales employed, indicating an upper limit for ex of 10-3• The deliquescence behaviour of crystalline HI03 and 1205 at 273 - 303 K, and the properties (e.g. water activity, density, viscosity, and efflorescence) of subsaturated and saturated iodate solutions were investigated. The deliquescence of 1205 and HI03 crystals at 293 K occurred at a relative humidity of 80.8 ± 1.0% and 85.0 ± 1.0% respectively. These values are consistent with measured water activity values for saturated 1205 and HI03 solutions at 293 K of 0.80 ± 0.01 and 0.84 ± 0.01 respectively. Optical and Raman microscope studies at low relative humidity indicate that 103- solution droplets do not exhibit efflorescence and may become ultra-viscous or glassy under atmospherically relevant conditions. In the presence of humic acid, 103- photo-chemically transforms to aqueous rand soluble iodinated humic acid and the fixing of iodine within humic structures is likely to occur at aromatic 1,2 diol groups. Transfer of 12 to the gas phase from the reduction of 103- to r, shows the oscillatory behaviour of the 'Bray-Liebhafsky' reaction and is enhanced in the presence of H202 and salinity (CI). The reduction of 103- to r shows first - order loss rate of (1.1 ± 0.1) x 10-5 s-1 which corresponds to a lifetime ~ 2 days for 103- in marine aerosol. This lifetime is consistent with the THAMOD model predictions. The predicted uptake coefficient of 03 (35 ppbv i.e. an atmospherically relevant concentration) on 100 nM I solution at 293 K was determined as (7.0 ± 0.2) x 10-7 with a resulting I2 flux of (2.9 ± 0.1) x 109 cm-2 s-1 which is ~ 5 times larger than the modelled flux at Sao Vicente (Cape Verde Island) in the tropical Atlantic Ocean. v
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available