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University of Oslo (UiO) (2010)

Formation of ozone due to chemical precursors and its impact on vegetation : Implementing WRF-Chem in parameterizing the dose of ozone to vegetation in the southern part of Africa

Rydsaa, Johanne Hope

Titre : Formation of ozone due to chemical precursors and its impact on vegetation : Implementing WRF-Chem in parameterizing the dose of ozone to vegetation in the southern part of Africa

Auteur : Rydsaa, Johanne Hope

Université de soutenance : University of Oslo (UiO)

Grade : Master Thesis in geoscience Discipline : Meteorology 2010

Résumé
Intense research during the past few decades has established that the todays background concentration of ozone can cause adverse effects on vegetation. These effects include reduction in crop yield, tree growth and species composition. One main objective of this thesis is to provide an estimate of the total stomatal dose of ozone to the vegetation of the Southern African area over a maize growing season. For this purpose the WRF-Chem model is implemented, a mesoscale weather prediction system, fully coupled with a chemistry module. To validate the model, results for the stomatal flux are compared to fluxes derived from eddy covariance data gathered in Castelporziano, Italy, during the spring and summer period of 2007. Implementing dependance on the evaporative power of the ambient atmosphere is found to reduce overestimation of the modelled stomatal flux during dry periods. The ozone concentrations simulated for Southern Africa are within the range of 20-45ppb, similar to those estimated for the same period by Zunckel et al.(2006). Peak values in the range of 70-100 ppb occured throughout the period, values well above the threshold levels at which plant damage can be expected. The stomatal flux of ozone is accumulated to yield the total stomatal dose of ozone to the vegetation across the domain over the full 7 month period. The highest doses are found in the south-eastern part of the modelled domain, exceeding 16mmol/m2 over the accumulation period. High doses reflects the combination of high mean ozone concentrations, sensitive landuse categories, and low mean temperatures due to high geographical elevation.

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