In large-scale models, an accurate calculation of energy fluxes at the lower boundary is important to ensure satisfactory predictions of the meteorological parameters. This work is performed using surface models.In this paper. various surface models. previously studied by Deardorff are tested against experimental data from the West African Monsoon Experiment 1979 in the Ivory Coast. Physical properties of the soil are assumed constant and uniform. Input variables are dry and wet bulb temperatures. wind velocity at the 2 m level, and global radiation. We compute sensible and latent heat fluxes and the surface conduction flux. A Crank-Nicholson scheme has been used with a time step of 5 min. Estimated sensible and latent heat fluxes agree well with experimental data. The order of magnitude of the difference between theoretical and experimental values is 30 W m-*for evaporation and 20 W m-* for sensible heat. Surface soil heat flux ie less satisfactorily calculated. which could result from properties assumed constant such as soil surface humidity. A model including the heat conduction in the soil provides the best results. The others, based on empirical formulations of surface soil heat flux, are less satisfactory. However. with a simple two-layer model. the predictions are quite acceptable.
The treatment of pesticides is a necessity in view of the stability and toxicity of the pesticides that generate them. The objective of this work is to study the degradation of picloram in aqueous medium under UV irradiation. It is a selective and systemic herbicide that can control woody plants and broadleaf weeds. The irradiations were carried out using a mercury vapor lamp of wavelength λ = 365 nm. A high performance liquid chromatograph equipped with a UV / visible detector was used to analyze the samples. The degradation of picloram in aqueous medium was carried out by direct photolysis and photocatalysis. In direct photolysis, a low rate of product degradation (6.9 %) was obtained after 225 min of irradiation. Photolysis in the presence of a catalyst (TiO2) accelerated the degradation of the molecule. Experiments demonstrating the effect of the concentration of the catalyst showed that the optimum concentration corresponding to a maximum degradation of picloram is 4 mg / L (62.68 %). The study of the influence of the pH of the solution on the degradation indicates that the molecule degrades better in an acid medium (pH = 5) with a rate of 62 % in 225 min -ISSN 1857-7431 518 of irradiation. Apparent order 1 degradation kinetics were observed in all cases.European Scientific Journal October 2017 edition Vol.13, No.30 ISSN: 1857 -7881 (Print) e Keywords: Picloram, Herbicide, Photolysis, Photocatalysis RésuméLe traitement des effluents phytosanitaires s'avère une nécessité vue la stabilité et la toxicité des pesticides qui les génèrent. L'objectif de ce travail est d'étudier la dégradation du piclorame en milieu aqueux sous irradiation UV. Il s'agit d'un herbicide sélectif et systémique qui permet de lutter contre les plantes ligneuses et les dicotylédones. Les irradiations ont été faites à l'aide d'une lampe à vapeur de mercure de longueur d'onde λ=365 nm. Un chromatographe liquide haute performance équipé d'un détecteur UV/visible a permis d'analyser les échantillons. La dégradation du piclorame en milieu aqueux a été réalisée par photolyse directe et par photocatalyse. En photolyse directe, un faible taux de dégradation du produit (6,9 %) a été obtenu après 225 min d'irradiation. La photolyse en présence de catalyseur (TiO2) a permis d'accélérer la dégradation de la molécule. Les expériences mettant en évidence l'effet de la concentration du catalyseur, ont montré que la concentration optimale correspondant à une dégradation maximale du piclorame est de 4 mg/L (62,68 %). L'étude de l'influence du pH de la solution sur la dégradation indique que la molécule se dégrade mieux en milieu acide (pH = 5) avec un taux de 62 % en 225 min d'irradiation. Des cinétiques de dégradation d'ordre 1 apparent ont été observées dans tous les cas.
In large‐scale models, an accurate calculation of energy fluxes at the lower boundary is important to ensure satisfactory predictions of the meteorological parameters. This work is performed using surface models. In this paper, various surface models, previously studied by Deardorff are tested against experimental data from the West African Monsoon Experiment 1979 in the Ivory Coast. Physical properties of the soil are assumed constant and uniform. Input variables are dry and wet bulb temperatures, wind velocity at the 2 m level, and global radiation. We compute sensible and latent heat fluxes and the surface conduction flux. A Crank‐Nicholson scheme has been used with a time step of 5 min. Estimated sensible and latent heat fluxes agree well with experimental data. The order of magnitude of the difference between theoretical and experimental values is 30 W m−2 for evaporation and 20 W m−2 for sensible heat. Surface soil heat flux ie less satisfactorily calculated, which could result from properties assumed constant such as soil surface humidity. A model including the heat conduction in the soil provides the best results. The others, based on empirical formulations of surface soil heat flux, are less satisfactory. However, with a simple two‐layer model, the predictions are quite acceptable.
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