Operational evaluation of air quality models.

This paper addresses the modeling and analysis of tropospheric ozone monitoring data for the assessment or "operational evaluation" of grid-based photochemical air quality model predictions. We first discuss general issues in the evaluation of gridded model predictions of pollutant concentrations against point field measurements and review currently recommended procedures for model evaluation. We then propose three new diagnostic procedures for model evaluation. These are: (1) spatio-temporal model based estimation of grid cell averages for comparison with model predictions, (2) graphical depiction and comparison of spatio-temporal correlation structures determined from the field monitoring data and from model output, and (3) diagnostic decompositions of the spatial fields of differences between model predictions and monitoring based estimates of grid cell average concentrations. These concepts are illustrated using field data from the SARMAP field study for the San Joaquin Valley in California and predictions from the SARMAP Air Quality Model.