2020: Sudden Decrease of the Dissolved Ozone Concentration in Sprays: A Mass Transfer Phenomenon?

Ozone is known to be a powerful oxidant with low persistence and has been shown to possess biocidal activity against a wide number of fungi and bacteria. These properties make ozone a good candidate as a substitute for chemical phytosanitary products in agriculture. However, when water containing dissolved ozone is sprayed, the concentration of ozone decreases dramatically with spraying distance. This study aims to better understand this ozone loss during spraying and, in particular, to identify whether mass transfer occurs. Identification was performed by dioxygen absorption and comparison of its concentration profiles with those for ozone desorption. Droplets were collected at different heights in the spray to measure the dissolved concentrations. Image analysis was used to determine the diameters and velocities of the droplets. Ozone self-decomposition kinetics were not able to explain the experimental concentration variation obtained in the droplets. The decrease of dissolved ozone in the liquid is then only caused by mass transfer. Most of the mass transfer seems to take place in the liquid sheet that leaves the nozzle. Volumetric mass transfer coefficients have been assessed for different regions of the spray. From mass transfer correlations, a model has been made to predict the concentration profile in droplets of the spray.