Some advanced models are seldom used in regulatory applications due to their complexity, long run-times and inability to model accurately at fine scales. Clearly this means that advanced models require more detailed meteorological input data to accurately emulate the complex dispersion effects. Advanced models can simulate the effects of coastal areas and terrain effects on pollutant transport and dispersion in a much more realistic way than a Gaussian-plume model, which assumes spatial uniformity in the meteorology. In situations of complex terrain or near coastal boundaries, significant changes in meteorological conditions can occur over short distances. In these situations an advanced dispersion model may be more suited to the situation and provide better results. This is likely to be especially true if pollutants cause effects at distances greater than about 10 kilometres from their source and under fumigation conditions. In such environments simple Gaussian-plume models may not provide the best results. The situation is further complicated by complex topography. Many of New Zealand's major cities are located within 20 kilometres of the coast and so the majority of air pollution concentrations over urban areas are affected by highly variable coastal airflows. The choice of an appropriate dispersion model is heavily dependent on the intended application. In choosing the most appropriate model it is very important to understand the model's limitations and apply it only to the situations that match its capabilities. In more complex atmospheric and topographical conditions, advanced puff or particle models and meteorological modelling may be required to maintain a similar degree of accuracy. This modelling accounts for the vast majority of dispersion modelling work in New Zealand. In medium-complex atmospheric and topographical conditions with relatively simple effects, Gaussian-plume models can produce reliable results. The width of the band associated with each model type is roughly proportional to the number of modellers currently using that particular type. Figure 2.1 illustrates the types of models typically applied to particular scenarios, depending on their scale and complexity. advanced models such as CALPUFF (Scire et al., 2000a) and The Air Pollution Model (TAPM) (Hurley, 2002).Gaussian-plume models such as AUSPLUME, ISCST3 (EPA1), AERMOD (EPA2) and CTDMPLUS (Perry et al., 1989).For regulatory purposes in New Zealand, there are two general types of dispersion models that can be used: the potential scale and significance of potential effects, including the sensitivity of the receiving environment (e.g.When choosing the most appropriate model the principal issues to consider are: One of the key elements of an effective dispersion modelling study is to choose an appropriate tool to match the scale of impact and complexity of a particular discharge. Publication Number: 671 Category(s): Air Number of pages: 91. Ausplume Gaussian Plume Dispersion Model Technical User Manual.

Ausplume user manual