A comparison of scavenging and deposition processes in global models: results from the WCRP Cambridge Workshop of 1995

We report on results from a World Climate Research Program workshop on repr esentations of scavenging and deposition processes in global transport mode ls of the atmosphere. 15 models were evaluated by comparing simulations of radon, lead, sulfur dioxide, and sulfate against each other, and against ob servations of these constituents. This paper provides a survey on the simul ation differences between models. It identifies circumstances where models are consistent with observations or with each other, and where they differ from observations or with each other. The comparison shows that most models are able to simulate seasonal species concentrations near the surface over continental sites to within a factor of 2 over many regions of the globe. Models tend to agree more closely over source (continental) regions than fo r remote (polar and oceanic) regions. Model simulations differ most strongl y in the upper troposphere for species undergoing wet scavenging processes. There are not a sufficient number of observations to characterize the clim atology (long-term average) of species undergoing wet scavenging in the upp er troposphere. This highlights the need for either a different strategy fo r model evaluation (e.g., comparisons on an event by event basis) or many m ore observations of a few carefully chosen constituents.