A comparison of aerosol total optical depths between models and (AERONET) observations might be interesting from the point that these models are designed to provide estimates on aerosol forcing. Discrepancies in total optical depth, however, reveal little about models, if their total aerosol optical depth is derived from individual contributions of sulfate, black carbon, organic carbon, dust and sea-salt. Thus, in order to explain, under-
stand and correct discrepancies to AERONET data and among models, evaluations on a sub-component basis become desirable, preferably at AERONET sites, where a particular component dominates. One of the major goals is the identification of off-setting errors. However, potential for offsetting errors even extends to the processing of each component. Most critical for the component treatment are model assumptions (of size and of humidification and ambient relative humidity) during the conversion of component mass into component optical depth.
After the presentation of model partitions of total aerosol optical depth into components, some background on the conversion of component mass to optical depth is provided. Then, each model's partition of aerosol mass is introduced, and from component data on optical depth and mass, effective mass-to-optical depth conversions are derived. Finally, in comparison of properties for large regions apparent trends of models will be summarized.
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