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CHOOSING A CHEMICAL MECHANISM FOR REGULATORY AND RESEARCH AIR QUALITY MODELING APPLICATIONS
Citation:
Luecken, D J. AND G. S. Tonnesen. CHOOSING A CHEMICAL MECHANISM FOR REGULATORY AND RESEARCH AIR QUALITY MODELING APPLICATIONS. Presented at 7th US-German Workshop, Bad Breisig, Germany, October 9-11, 2002.
Impact/Purpose:
The objective of this research is to develop chemical mechanisms that accurately represent the complex atmospheric chemistry involved in the formation of ozone and other, related, photochemically- produced pollutants such as secondary air toxics and organic aerosol precursors. This task will produce updated, state-of-the-art photochemical mechanisms, support the evaluation of these mechanisms with experimental data, and apply these mechanisms for regulatory and research purposes in emissions and observations-based models. The application of the models to provide scientific support for VOC-reactivity based ozone control policies will be a major focus of this task. The dissemination of results of model applications in this area (both ours and those from outside agencies) via the US German workshop agreement, are also supported as a small portion of this task. While this task primarily focuses on ozone-related issues, our mechanism development and evaluation will consider that these mechanisms should also be able to adequately predict the concentrations of other related photochemical species. This task is being performed in close collaboration with Task 12043, "Reducing Uncertainty in the Chemical Mechanisms of Aromatic and Biogenic Hydrocarbons" and Task 20461, "FY05 CMAQ Release."
Description:
There are numerous, different chemical mechanisms currently available for use in air quality models, and new mechanisms and versions of mechanisms are continually being developed. The development of Morphecule-type mechanisms will add a near-infinite number of additional mechanisms to this list. Choosing among these mechanisms is a difficult task. The chemical mechanism that you choose has a huge influence on the accuracy of the results as well as the computer resources required for the simulations. Thus, it is important that an appropriate mechanism be chosen for the type of simulation being performed, with a consideration of the species that you are interested in, as well as the temporal and spatial resolution required of the simulation. This talk will focus on the types and versions of chemical mechanisms available for 3-D air quality modeling studies of regional and urban gaseous air pollution, including updates to older mechanisms and Morpho-type mechanisms. We will summarize evaluations and intercomparisons of mechanisms, including specific chemical entities that must be compared in order to truly test mechanisms. Our recommendations for intercomparison of mechanisms utilize Process Analysis and Integrated Reaction techniques which allow the modelers to understand not only what the differences are among mechanism predictions, but why these differences occur. Model inconsistencies can be traced back to original radical formation and loss processes, and reactions with high uncertainties can be pinpointed for further study. We will discuss examples of in-depth comparisons of specific chemical mechanisms, research needs for evaluating new mechanisms, and the development of a protocol consisting of a recommended, standard set of tests that can be used to analyze the performance of a chemical mechanism and to compare two or more mechanisms.
This work has been funded in part by the United States Environmental Protection Agency under PO 9D1000NAEX to the University of California, Riverside. It has been subjected to Agency review and approved for publication.