"small System" Modelling of the Polluted Planetary Boundary Layer.

Available from UMI in association with The British Library. Requires signed TDF. The transport, chemical transformation, emission and deposition of trace constituents of the Planetary Boundary Layer (PBL) is described. Simplified schemes for describing this behaviour are discussed and the idea of a small systems approach put forward. This approach hypothesises that there are regions of the total theory domain which are sufficiently independent of other areas that they can be described by restricted domain models. Explicit recognition of output applicability is required if the model is to be used successfully. Two small systems models, describing volatile nitrate aerosol kinetics and surface ozone in an urban plume, are used as case studies to test the method. Ammonium nitrate aerosol is shown to have a significant kinetic restraint on the attainment of the dissociation equilibrium in the PBL. This will have important repercussions on the spatial distribution of nitrate deposition. The effect of input parameters on incremental ozone concentrations within urban plumes are quantified using a factorial experimental design procedure. Considerable non-linear interactions are observed between parameters. The extreme ozone increments measured in the field are not simulated by the model used, and the variation of neither structural nor input parameters adjusts the model sufficiently to account for these large incremental ozone effects. The above results can be regarded as a pragmatic justification of the small systems approach, and its legitimacy is made more apparent when it is viewed as an intermediary expression in a hierarchy of idealisational statements concerning the PBL. The classical rate law for a bimolecular process can be concretised using a set of correctional functions to give the small system model, the Lagrangian model, the Eulerian and the (fully-concretised) continuity equation at various points. The hierarchy of air pollution models, and the applicability of their output is thus made clear.