Preliminary results From a partial LRTAP model based on an existing meteorological forecast model

An existing state‐of‐the‐art regional meteorological model is coupled through appropriate constituent mass conservation equations to model the long‐range transport of atmospheric pollutants (LRTAP) under restrictive constraints on atmospheric chemistry and deposition. Particular emphasis is given to the importance of a good representation of turbulence and other sub grid‐scale processes in the planetary boundary layer (PBL), both in the formulation and in the interpretation of the results. The regional meteorological model provides not only forecasts of wind velocity and temperature, but also vertical diffusion profiles consistent with the evolution of its PBL. The transport in the LRTAP model is handled by computationally stable algorithms such that the time step may be chosen on the basis of accuracy rather than stability, and the chemistry is described by a simple four‐species model of the oxidation of sulphur dioxide and nitrogen dioxide. Results are presented of a sample 48‐h summer simulation over central and eastern North America, using real meteorological data and time‐averaged emission inventory data; parameters of the integration include a one‐hour time step, a horizontal resolution of 100 km and 15 variably spaced vertical levels, 10 of which are contained in the lower one third of the atmosphere. It is argued that despite the simplicity of the chemistry, the results are qualitatively realistic and the high impact of the PBL processes on LRTAP is evident. For this particular simulation, it is interesting to note the existence of a region over Nova Scotia where the deposition of sulphates is significantly greater than that which could be expected from local sources. This is interpreted as being due to the confluence of two flows that pass over two different centres of high emission ofSC>2, andas being evidence of the model's ability to qualitatively model LRTAP.