Along with the statistical measures, EPA recommends that the following
four sets of graphical displays be prepared and included as part of the performance analysis.
• Time series plots of model and predicted hourly ozone for each monitoring location in the
nonattainment area, as well as key sites outside of the nonattainment area. These plots can
indicate if there are particular times of day or days of the week when the model performs
especially poorly. Figure 18.1 shows a sample time series plot. This graphic was
developed using the air quality analysis module of the Atmospheric Model Evaluation
Tool (AMET) (Appel, 2005), though other evaluation tools exist and can be used.
Figure 18.1. Sample time series analysis plot for a 12-km model vs. observed 2001 case. The
upper plot shows a particular analysis for 1-hour maxima ozone, July through September
performance averaged over five sites in Cleveland, Ohio. The bottom plot shows the bias and
error (percentage) calculated based on the predicted 1-hour maxima ozone from the upper plot.
• Scatter plots of predicted and observed ozone at each site within the nonattainment area
(and/or an appropriate subregion). These plots should be completed using: a) all hours
within the modeling period for hourly ozone, and b) all 8-hour daily maxima within the
modeling period. It may also be useful to develop separate plots for individual time
periods or key subregions. These plots are useful for indicating if there is a particular part
of the distribution of observations that is poorly represented by the model49. See Figure
18.2 below for a scatter plot example, which was generated using the AMET.
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