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 representations ofscavenging and deposition processes in global transport models of the atmosphere. 15 modelswere evaluated by comparing simulations of radon, lead, sulfur dioxide, and sulfate against eachother, and against observations of these constituents. This paper provides a survey on the simulationdifferences between models. It identifies circumstances where models are consistent withobservations or with each other, and where they differ from observations or with each other. Thecomparison shows that most models are able to simulate seasonal species concentrations nearthe surface over continental sites to within a factor of 2 over many regions of the globe. Modelstend to agree more closely over source (continental) regions than for remote (polar and oceanic)regions. Model simulations differ most strongly in the upper troposphere for species undergoingwet scavenging processes. There are not a sufficient number of observations to characterize theclimatology (long-term average) of species undergoing wet scavenging in the upper troposphere.This highlights the need for either a different strategy for model evaluation (e.g., comparisons onan event by event basis) or many more observations of a few carefully chosen constituents.