Testing and improving the EMEP ozone deposition module

This study evaluates the ozone deposition module developed for the European Monitoring and Evaluation Programme photochemical transport model. The module allows an estimation of both total and stomatal ozone flux to different vegetation types, taking into account plant phenology and environmental conditions. Based on a series of model tests against micrometeorological measurements of ozone fluxes, including data on stomatal conductances, the performance of the land-cover specific parameterisations was assessed and improvements implemented. Tests were carried out for coniferous forest, moorland and wetland ecosystems in Northern Europe, and for a wheat field and a grassland site located in Southern Europe. The improvements consisted of a needle age factor for coniferous forests, revised ground surface conductances, and a new leaf-to-canopy up-scaling method for wheat. These resulted in better agreement with observed surface conductances and deposition velocities, although a number of discrepancies are noted. In general, the parameterisation of non-stomatal deposition and the performance of the module under high soil moisture deficits were identified as key uncertainties requiring further investigation.