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Background: Hygroscopic salts are often applied as foliar fertilizers and calcium (Ca) salts have been used as model for cuticular permeability studies, with focus on their Point of Deliquescence (POD). Aim: This study was aimed at characterizing water sorption and desorption processes at 20, 30, and 40°C temperature (T), of two model Ca salts commonly used as foliar sprays. Methods: Trials were developed with pure Ca-chloride and Ca-nitrate salts in addition to 2 M and 150 mM Ca solutions. Salts were analyzed by Dynamic Vapour Sorption (DVS) and climate chamber experiments. Results: For both Ca salts, water sorption and desorption processes followed hysteresis curves which varied with T. Salt POD was T-dependent and generally decreased with increasing T. For both Ca salts, the process of efflorescence began at or below 10% RH, at a certain level of water desorption Ca-salts becoming highly concentrated solutions (HCS). Conclusions: Owing to the low point of efflorescence (POE) of both salts, drops of Ca-chloride and Ca-nitrate supplied as foliar sprays will not fully dry under normal RH and T conditions in most world areas. Both Ca salts have a similarly high foliar penetration potential despite their different POD. The significance of the results for the potential absorption of foliar fertilizers and salts by the foliage is discussed under an agronomic and eco-physiological viewpoint., Facultad de Ciencias Agrarias y Forestales

International audience; The Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus/Solar Occultation at Infrared (SPICAV/SOIR) suite of instruments onboard the Venus Express spacecraft comprises three spectrometers covering a wavelength range from ultraviolet to midinfrared and an altitude range from 70 to >100 km. However, it is only recently (more than 1 year after the beginning of the mission) that the three spectrometers can operate simultaneously in the solar occultation mode. These observations have enabled the study of the properties of the Venusian mesosphere over a broad spectral range. In this manuscript, we briefly describe the instrument characteristics and the method used to infer haze microphysical properties from a data set of three selected orbits. Discussion focuses on the wavelength dependence of the continuum, which is primarily shaped by the extinction caused by the aerosol particles of the upper haze. This wavelength dependence is directly related to the effective particle radius (cross section weighted mean radius) of the particles. Through independent analyses for the three channels, we demonstrate the potential to characterize the aerosols in the mesosphere of Venus. The classical assumption that the upper haze is only composed of submicron particles is not sufficient to explain the observations. We find that at high northern latitudes, two types of particles coexist in the upper haze of Venus: mode 1 of mean radius 0.1 ≤ rg ≤ 0.3 μm and mode 2 of 0.4 ≤ rg ≤ 1.0 μm. An additional population of micron-sized aerosols seems, therefore, needed to reconcile the data of the three spectrometers. Moreover, we observe substantial temporal variations of aerosol extinction over a time scale of 24 h.