A multi-trajectory chemical-transport vectorized gear model: 3-D simulations and model validation

A new multi-trajectory highly vectorizable Gear chemical-transport model is discussed and tested against measurements from 25 sites in Europe for a two-week summer period. The simulations are compared with measurement data and with results of a Quasi-Steady-State Approximation (QSSA) based Lagrangian model using the EMEP mechanism. The model is developed from the Lagrangian EMEP model. The Regional Atmospheric Chemistry Mechanism (RACM) is used as the model's chemical mechanism. To solve the stiff chemical rate equations, a sparse-matrix highly vectorizable Gear algorithm is used. The meteorological data used to run the model are obtained from the HIgh Resolution Limited Area Model (HIRLAM). The vectorized Gear based model improves the accuracy of the numerical solution for the chemistry compared with the QSSA based model. The differences between the two models are explained by alternative approaches of the chemical modules employed in the model: a Gear algorithm versus a QSSA solver, photolysis rate parameters in RACM are calculated from a radiation transfer code versus parameterized photolysis rate parameters used in the Lagrangian EMEP model, the RACM versus the EMEP atmospheric chemical mechanisms and two methods of aggregating the emissions of Volatile Organic Compounds (VOC). Photolysis rate parameters calculated from radiation codes (which are more accurate than simple parameterizations) and the Gear algorithm (which is a benchmark solver compared with the QSSA solver) are recommended for atmospheric chemistry modeling because of the high sensitivity of ozone concentrations to the chemical reaction scheme and to the photolysis rates (Stockwell and Goliff, 2004). © Springer Science + Business Media, Inc. 2005.