Joyce Penner (PI)
University of Michigan Ann Arbor
penner@umich.edu

Development of a Coupled Aerosol-Chemistry Model for GMI

The role of aerosols in climate forcing has been established as a critical factor in climate change. In this respect the role of aerosols in the indirect effects on clouds and the role of black carbon and organic matter in determining both the direct and indirect effects are perhaps the most uncertain aspect, though the volatile products nitrate and ammonium may also be significant. The key to understanding the effects of aerosols lies in understanding the chemically-resolved size distribution as well as the vertical distribution of aerosols. Here, we propose to add a set of process modules that are able to treat the formation of secondary organic aerosols and the volatile aerosol components nitrate and ammonium to the GMI model. The development of secondary organic aerosols will be treated using the Sillman fast photochemical mechanism, which is able to accurately represent the full suite of chemical reactions needed to treat these components. Moreover, we will improve the fast dynamic aerosol module that is presently being added to the GMI model by including a new set of nucleation mechanisms and by expanding its capability to better treat the aerosol size distribution. Here, we propose to apply the combined aerosol/chemistry GMI model (and extensions of this model) to understand the processes determining the aerosol size distributions and vertical profiles and to explore how different treatment of chemistry might impact aerosol dynamics.  Our current aerosol modules (which have been implemented in our 3-D model IMPACT) treat the mass-transport limited aerosol/gas equilibrium processes as well as nucleation, condensation of low vapor pressure gases, and coagulation. The focus of our previous efforts has been to develop aerosol process modules that are fast and yet accurate and that can be added to global aerosol models to accurately treat both homogeneous chemistry and heterogeneous chemical processes in the upper troposphere. We have also developed a detailed gas phase chemical mechanism that is necessary to understand ozone formation on regional and urban scales. Recent studies have shown that our chemical treatment has important consequences for the global scale. Here, we plan to couple a gas-phase chemistry version of the GMI model that includes our fast photochemical module to our aerosol modules to understand the chemical and physical processes that determine the evolution of the chemically-resolved aerosol size distribution which is so important for climate effects.

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