A procedure for inter-comparing the skill of regional-scale air quality model simulations of daily maximum 8-h ozone concentrations

An operational model evaluation procedure is described to quantitatively assess the relative skill among several regionalscale air quality models simulating various percentiles of the cumulative frequency distribution of observed daily maximum 8-h ozone concentrations. Bootstrap sampling is used to characterize the variability in the observed percentile values, thereby providing a means for assessing whether the differences seen between model predictions are significant. The procedure was designed to facilitate model inter-comparisons, since all that is needed to implement the procedure is for each modeler to provide a listing of the daily maximum 8-h ozone concentration predictions for a summer season for grid cells containing ozone monitors. Available ozone modeling results for the summer of 2002 from four regional-scale air quality simulations are used here to illustrate the results that can be obtained. These simulations were conducted using the Community Multi-Scale Air Quality (CMAQ) model with somewhat different setups. The modeling domains were different, but there is a region in the central Eastern United States where ozone estimates from all four simulations are available. Our objective is to describe the inter-comparison procedure, to illustrate the results obtained, and to stimulate discussions on how similar procedures might be developed and improved in the future. Published by Elsevier Ltd.