Heterogeneous Chemistry: Understanding Aerosol/Oxidant Interactions

Joyce E. Penner
Department of Atmospheric, Oceanic, and Space Sciences
University of Michigan
Ann Arbor, MI 48209
734-936-05190
fax 734-764-5137
penner@umich.edu

One of the most important advancements needed in global chemical transport models is the development of models that are capable of treating both gas phase and heterogeneous chemistry. For example, we know that the absorption of HNO₃ and reaction within aerosols can significantly deplete HNO₃ from the gas phase. These reactions deplete NO_x and hydroxyl radicals, both of which are directly tied to ozone formation processes. At the same time, the formation of HNO₃ and its partitioning into the aerosol phase can significantly increase total aerosol mass and surface area available for reaction. This example shows that gas/aerosol interactions may be important to study in order to predict the gas phase concentrations of O₃ and other oxidants. It is also important to include gas phase processes in models that predict aerosol concentrations. For example, the production of H₂O₂ by HO₂ and the depletion of H₂O₂ within clouds and in the gas phase by reaction with SO₂ alters the rate of formation of sulfate aerosols, one of the most important aerosol types. The rate of formation of organic aerosols formed as a result of the oxidation of gas phase precursors also depends on gas phase chemistry. Here, we propose to examine these interactions in a fully coupled aerosol/gas phase chemistry model. The model will be used to explore a number of uncertain aspects of heterogeneous interactions in order to help guide and focus laboratory and field studies. Also, the model will be used to examine the importance of including these interactions for determining ozone and aerosol concentrations at regional scales. This information can also be used to inform the models that treat the chemistry of ozone and aerosols at these regional and local scales of the appropriate initial and boundary conditions under a variety of emissions scenarios.

Some further information can be found in the viewgraphs from a presentation at the Atmospheric Sciences Program Annual Meeting held in February 2001. An update can be found in the viewgraphs from a presentation at the Atmospheric Sciences Program Annual Meeting held in March 2002.