United States Environmental Protection Agency Office of Research and Development National Exposure Research Laboratory FY02 Research Abstract Government Performance Results Act (GPRA) Goal 1.1.8 APM14 Significant Research Findings: Update a Faster, More Detailed Approach (Morphecule Mechanism) for Modeling Atmospheric Chemistry and Work with EPA Staff To Implement the Mechanism in the Agency's Principle Air Quality Model Air quality models that realistically describe the photochemical formation of ozone, particulate matter (PM), and other pollutants, such as air toxics and pesticides, are needed by the U.S. Environmental Protection Agency (EPA) and state agencies to develop risk management strategies to decrease their concentrations to safe levels. The atmospheric chemistry of ozone involves the complex interactions of thousands of different chemical reactions, while that of secondary organic particulate matter involves significantly more. For emerging pollutants that EPA will need to address now and in the future, such as secondary toxic compounds or organic aerosols, it will be necessary to account for even more reactions. Scientific Problem and Policy Issues Including this complex chemistry in a current urban-to-regional air quality model would swamp even the most powerful computers available; therefore, the chemistry in current models is always extremely simplified. Air quality models must represent the thousands of reactions that actually occur in the atmosphere by only about 80-200 model reactions, and sometimes less. While these simplifications allow the model to run efficiently, they can result in inaccuracies in some of the model predictions. To address this problem, we have developed a way to perform these calculations more efficiently, but without losing accuracy in the predictions. This method, the Morphecules approach, can efficiently and realistically describe the complex atmospheric chemistry of ozone and other photochemical pollutants in regulatory and research air quality models. This will allow us to develop pollution control strategies in a more holistic manner, and integrate control strategies for all important species simultaneously. Research The Morphecules approach assigns individual chemical species into a small Approach number of groups in the air quality model based on their structure and reaction characteristics. The computer intensive parts of the air quality model are performed on these groups, which allows the model to run faster National Exposure Research Laboratory — November 2002 ------- because the computations are performed on a smaller number of components. The model remembers the individual chemical species within each group, their initial concentrations before being added to the group, and their reaction rates, so that they can be recreated from the group and their concentrations updated at the end of the time step. This allows the model to retain detailed information about the atmospheric chemistry of ozone and other photochemical reactants, yet still efficiently use computer resources. Under this project, the software to implement the Morphecules approach was delivered to run on a PC and was ported to a UNIX machine. Substantial modifications were made to the code to enable it to be executed under a UNIX-based operating system. The software was linked to a box model version of the CMAQ/Models3 air quality model. The first step was to develop, debug, and implement libraries and driver routines to allow the code to be run in a purely explicit mode, where all species were introduced to the chemical solver without any grouping. Following that, additional work was done to utilize the full capacity of the code, using the grouping and ungrouping routines to speed up the computational solution. A demonstration test was performed on a detailed chemical mechanism for a family of aldehyde compounds. Results and This work resulted in a highly modified set of compiler, solver, and library Implications driver routines that are demonstrated to run within a 1-dimensional box model version of CMAQ. All code modifications have been documented extensively within the code, as well as summarized in a final report. The code and report of modifications were delivered on May 24, 2002. The software modifications and additional interface codes developed in this project will allow more complex representations of atmospheric chemistry to be used in the CMAQ code being developed at EPA for regulatory and research purposes. By implementing this complex chemistry using Morpho- type solvers, we will be able to run highly detailed descriptions of the atmospheric chemistry of ozone, secondary particulate matter, and secondary air toxics in full, 3-D simulations. Initial execution of the Morphecules code has shown that it is possible to produce and utilize a highly efficient, accurate, and user-friendly method for incorporating complex atmospheric chemistry to represent the chemistry that occurs in the atmosphere and to incorporate it into air quality models. National Exposure Research Laboratory — November 2002 ------- Research The code was developed under collaboration with the University of North Collaboration Carolina, Chapel Hill funded by contract 68D50129, and implementation of and Publications ^ C0(je jnt0 CMAQ was performed under contract #68-W7-0055 with Lockheed Martin Services, Inc. Future Research The next step of the implementation will be extension of this work from the 1-D version of CMAQ to the fully 3-D CMAQ. Additional tests will be performed to verify that the computational calculations are accurate and efficient. For additional information contact: Deborah Luecken U.S. EPA, Office of Research and Development National Exposure Research Laboratory, Maildrop D205-03 Research Triangle Park, NC 27711 Phone: 919/541-0244 Email: luecken.deborah@epa.gov Contacts for Additional Information National Exposure Research Laboratory — November 2002 ------- |