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TESTING PHYSICS AND CHEMISTRY SENSITIVITIES IN THE U.S. EPA COMMUNITY MULTISCALE AIR QUALITY MODELING SYSTEM (CMAQ)
Citation:
Arnold, J. R. AND R L. Dennis. TESTING PHYSICS AND CHEMISTRY SENSITIVITIES IN THE U.S. EPA COMMUNITY MULTISCALE AIR QUALITY MODELING SYSTEM (CMAQ). Presented at 27th NATO/CCMS International Technical Meeting on Air Pollution Modeling and its Application, Banff, AB, CANADA, October 25 - 29, 2004.
Impact/Purpose:
The goal of this task is to thoroughly characterize the performance of the emissions, meteorological and chemical/transport modeling components of the Models-3 system, with an emphasis on the chemical/transport model, CMAQ. Emissions-based models are composed of highly complex scientific hypotheses concerning natural processes that can be evaluated through comparison with observations, but not validated. Both performance and diagnostic evaluation together with sensitivity analyses are needed to establish credibility and build confidence within the client and scientific community in the simulations results for policy and scientific applications. The characterization of the performance of Models-3/CMAQ is also a tool for the model developers to identify aspects of the modeling system that require further improvement.
Description:
Uncertainties in key elements of emissions and meteorology inputs to air quality models (AQMs) can range from 50 to 100% with some areas of emissions uncertainty even higher (Russell and Dennis, 2000). Uncertainties in the chemical mechanisms are thought to be smaller (Russell and Dennis, 2000) but can range to 30% or more as new techniques are applied to re-measure reaction rate constants and yields. Single perturbation sensitivity analyses have traditionally been used with AQMs to characterize effects of these uncertainties on peak predicted ozone concentration ([O3]).
However, confidence in AQM applications depends on understanding the physical and chemical model dynamics in full emissions cases and in cases with proposed controls on oxides of nitrogen (NO+NO2=NOx) and/or volatile organic compounds (VOC). With a sensitivity analysis, emissions control runs depict the true photochemical system change which we define as the O3 control response, deltaO3/deltaENOx and deltaO3/deltaEVOC, where deltaENOx or deltaEVOC is the type and amount of control required to reduce O3 to acceptable levels. The model's most important sensitivity, correspondingly, is how its control response is changed by uncertain inputs and parameters, not simply how the resultant [O3] might be changed by the uncertainties in a full emissions case. We define that latter quantity as DeltaO3, or the change in [O3] due only to the uncertainty perturbation with full emissions.
This work was performed under a Memorandum of Understanding between the U.S. Environmental Protection Agency (EPA) and the National Oceanic and Atmospheric Administration (NOAA) of the U.S. Department of Commerce and under agreement number DW13921548. Although it has been reviewed by EPA and NOAA and approved for publication, it does not necessarily reflect policies or views of either agency.