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DEVELOPMENT OF AN AGGREGATION AND EPISODE SELECTION SCHEME TO SUPPORT THE MODELS-3 COMMUNITY MULTISCALE AIR QUALITY MODEL
Citation:
Cohn, R. D., B K. Eder, S K. LeDuc, AND R L. Dennis. DEVELOPMENT OF AN AGGREGATION AND EPISODE SELECTION SCHEME TO SUPPORT THE MODELS-3 COMMUNITY MULTISCALE AIR QUALITY MODEL. JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY 40(2):210-228, (2001).
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:
The development of an episode selection and aggregation approach, designed to support distributional estimation of use with the Models-3 Community Multiscale Air Quality (CMAQ) model, is described. The approach utilized cluster analysis of the 700-hPa east-west and north-south wind field components over the time period of 1984-92 to define homogeneous meteorological clusters. Alternative schemes were compared using relative efficiencies and
meteorological considerations. An potimal scheme was defined to include 20 clusters 9five per season), and a stratified sample of 40 events was selected from the 20 clusters using a systematic sampling technique. The light-extinction coefficient, which provides a measure of visibility, was selected as the primary evaluative parameter for two reasons. First, this parameter can serve as s surrogate for particulate matter with diameter of less than 2.5 m, for which few observational data exists. Second, of the air quality parameters simulated by CMAQ, this visibility parameter has one of the most spatially and temporally comprehensive observational datasets. Results suggested that the approach reasonably characterizes synoptic-scale flow patterns and leads to strata that explain the variation tin extinction coefficient and other parameters (temperature and relative humidity) used in this analysis, and therefore the approach can be used to achieve improved estimates of these parameters relative to estimates obtained using other methods. Moreover, during seasonally based clusters further improves the ability of the clusters to explain the variation in these parameters and therefore leads to more precise estimates.
The work reported in this document was funded wholly or in part by the U.S. Environmental Protection Agency. The document has been reviewed and approved by the agency for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.