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Atmospheric Composition

Global models are beginning to include processes that depend on detailed aerosol properties to better represent direct and indirect climate forcing. New aerosol representations include aerosol number, surface area, composition, and mixing state. However, the detailed processes represented in the models have now far surpassed the quality of model inputs. Since these properties are not given for emissions, the aerosol fields are not initialized correctly. Furthermore, the aerosol properties that are measured directly at emission are different from those that a large model should use. Global model grid boxes range from about 100 km to 500 km in scale, while changes in aerosol properties occur over much smaller distances (“sub-grid scales”). The objective of this proposal is to produce an Emission-to-Global-Grid Transfer Routine for Aerosol Microphysics which accepts any set of global emission inventories and land characterization, and produces a suitable average of aerosol microphysical and chemical properties over a global model grid-box. Sensitivities of direct and indirect radiative forcing to aerosol properties will be tested using a global transport model, and the transfer routine will be optimized to represent the sensitive properties. The aerosol representation will be evaluated both near and far from emission regions using in-situ and remote-sensing measurements. The routine will be compatible with hindcast models and future projections, because input parameters will be either observable or predictable. End-users will be able to demand outputs for any aerosol microphysical scheme, and the routine will comply with ESMF practice. Finally, we will use the improved model to examine the net direct and indirect climatic effects of high-density emission regions (megacities or industrial areas), specific source regions, and specific source categories. METHODS: We will develop a “bottom-up” representation of aerosol processes within a model grid box. Tools to be used are: (1) An interface with an extensive emission data set of Aerosol Mass Spectrometer data on size and chemical composition; (2) Emission distributions using an emission estimating program developed at UIUC (SPEW) combined with MODIS 1km land-cover data; (3) Ensembles of a Lagrangian model (PartMC-MOSAIC) which resolves microphysical, chemical and thermodynamic information about single particles, and which can be averaged to parameterize process rates within a grid box sized for a global model. Results Results will be evaluated by comparison with apparent microphysical properties inferred from AERONET, with data from intensive field studies, and by using Level-2 (fine scale) MODIS data to evaluate gradients in aerosol optical depth. We will also examine the question of microphysics from the top down using a global chemical and transport model (GISS ModelE). We will also determine the aerosol characteristics to which direct and indirect forcing of climate, aerosol optical depth, and aerosol removal are most sensitive. These sensitivity studies will be evaluated by determining which model results are most consistent with aerosol properties and total optical depth using AERONET and MODIS data. SIGNIFICANCE: The work proposed here results in improved models which will answer NASA’s science questions, “How is the global Earth system changing?” and “How will the Earth system change in the future?” Strengthening the link between emissions and global models is required to understand and improve predictive capability for changes in climate forcing and air quality associated with atmospheric composition. This work will improve how spatial and temporal evolution of aerosol is represented in CTMs by improving processes and assessing models against observations. The model components developed herein must be tested on present-day data, but will be designed to link both hindcast simulations and future emission predictions.

Project PI: Tami Bond/University of Illinois at Urbana-Champaign

3230c Newmark Civil Engineering Laboratory 205 N. Mathews Ave. Urbana, IL 61801

Phone: (217) 244-5277

Fax: (217) 333-6968

Email: yark@illinois.edu

http://cee.illinois.edu/node/95

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Started: Aug 10, 2010

Last Activity: Dec 15, 2010

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