Development and Application of a Reactive Plume-in-grid Model: Evaluation over Greater Paris

Classical air quality models at regional scale, based on Eulerian gridded approaches, suffer from several limitations when applied to the dispersion of elevated point emissions (e.g. from power plant stacks). In particular, emissions from point sources are assumed to mix immediately within a grid cell, whereas a typical point-source plume does not expand to the size of the grid cell for a substantial time period. In addition, the incorrect representation of concentrations within the plume leads to a poor estimation of the chemical reaction rates, in the case of reactive plumes. The plume-in-grid method is a multiscale modeling technique that couples a Gaussian puff model with an Eulerian model in order to better represent these emissions. We present the reactive plume-in-grid model developed in the air quality modeling system Polyphemus, and its evaluation for photochemical applications. The chosen application domain is the Ile-de-France region, during six months (summer 2001). There were 89 major point sources selected for the subgrid-scale treatment. Comparisons are made between the results with the Eulerian model alone, and with the plume-in-grid treatment. The analysis is based both on global results for the whole period, and on a few selected days of interest. A sensitivity study is also carried out, especially to point out the influence of the local-scale parameterizations.