Evaluation of Tropospheric Aerosol Microphysics Simulations Using Assimilated Meteorology and Field Campaign Observations

A major goal of global aerosol modeling is the prediction of aerosol number concentrations and size distributions that will contribute to determination of cloud condensation nuclei (CCN) and ultimately estimation of the aerosol indirect effects, which are still very uncertain. To date, field campaigns provide the most detailed observations of aerosol microphysical behavior. Meaningful model-observation comparisons require assimilated meteorology so simulations reproduce the specific meteorological or pollution events of a given field campaign. To this end, the TwO-Moment Aerosol Sectional (TOMAS) microphysical algorithm is integrated into the GEOS-CHEM model, a global three-dimensional model of tropospheric chemistry driven by assimilated meteorological observations from the Goddard Earth Observing System (GEOS). TOMAS in GEOS-CHEM improves the previous aerosol model by tracking aerosol evolution on a microphysical basis. TOMAS algorithm conserves both number and mass concentrations of aerosol segregated into 30 size bins. The microphysical processes include coagulation, condensation, evaporation, nucleation, size-resolved wet deposition and size-resolved dry deposition. To test the aerosol model, the model predictions will be compared with the observational data from the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) and Transport and Chemical Evolution over the Pacific (TRACE-P) experiment carried out during the spring of 2001. The various aspects of aerosol behavior that will be investigated are the model treatment of primary ultrafine aerosol emissions, predictions of aerosol vertical profiles, and the nucleation parameterization.