Diagnostic Analysis of CMAQ Dry Deposition Fields in the Context of AQMEII4

Phase 4 of the Air Quality Model Evaluation International Initiative (AQMEII4) is focused on the diagnostic intercomparison and evaluation of deposition simulated by regional-scale air quality modeling systems and employs both grid and box modeling techniques to accomplish this goal. This study presents an analysis of CMAQv5.3.1 simulations that were performed in the context of AQMEII4 over a North American modeling domain. Results show that variability in the estimated dry deposition sink affected model performance and resulted from both differences in model process formulation and the representation of the underlying land use (LU). To gain mechanistic insights into model behavior, the study employs diagnostic variables defined for the AQMEII4 project, i.e., grid scale and land-use specific effective conductances and deposition fluxes for the major dry deposition pathways (stomatal, cuticular, lower canopy, and soil). Analysis of these variables indicates that there generally is a greater contribution to ozone dry deposition from the stomatal and cuticular pathways in the CMAQ M3DRY dry deposition scheme compared to CMAQ STAGE dry deposition scheme and that differences in LU classification schemes can have a pronounced impact on simulated fluxes.