EVOLUTION AND FUTURE OF DISPERSION MODELS IN AUSTRALIA AND NEW ZEALAND

David Rollings1, Michael Burchill1, Dylan Turnbull1

1 AECOM, Newcastle, Australia

1. Introduction

Dispersion models have been used in Australia as a tool for assessing air quality impacts for over 50 years, with the earliest assessments undertaken in the 1940’s using simple gaussian plume equations to predict stack emissions downwind of emission sources. Since these earliest assessments, a range of factors have led to development of new and more complex impact assessment tools.

Over the past half century, air dispersion models utilized in Australia and New Zealand (ANZ) have undergone continuous improvement due to various scientific factors. These factors include a deeper understanding of plume dispersion science, the influence of meteorology on pollutant transport, and the ever-growing computational capacity available when running dispersion models. These advancements have contributed to the ongoing enhancement of air dispersion models employed in ANZ.

The development and utilization of dispersion models in Australia and New Zealand have also been influenced by various non-technical factors. These factors include the influence and experiences from other countries, particularly the United States and, to a lesser extent, Europe. The development of guidance documents and the evolution of state and regional regulatory frameworks within Australia and New Zealand have also played a significant role in shaping the development and application of dispersion models in the region.

Over time, these (and other) technical and nontechnical drivers have led to the development of both new or improved dispersion models and dispersion modelling techniques utilised across ANZ. Understanding these drivers for change can be valuable when trying to understand where dispersion modelling may progress in the future and be ready for those changes.

This paper aims to understand the following:

 History of dispersion model development.

 What factors have influenced the development of new models?

 What factors have changed that may influence the development of models in the future?

 How do the current dispersion models reflect the factors that are shaping the future of dispersion modelling?

 Can a future dispersion modelling trend be identified to lead the development of new models or prepare for the implementation of new models?

2. History of dispersion model development

The history of air dispersion modelling (ADM) in ANZ is inextricably linked with the international history of dispersion modelling, tracing back to the early 20th century. A timeline of the major modelling milestones is discussed below along and presented graphically in Figure 1.

2.1. Early dispersion model developments

The history of dispersion models dates back over a century to the development of the Gaussian Plume equation by Lewis Fry Richardson in 1918 and the development of empirical plume behaviour equations by Gordon A. Taylor in the early 1940’s.

The empirical equations developed by Taylor were the first attempts at deriving a relationship between stack plume characteristics (stack height, stack velocity and atmospheric stability) and the behaviour of plumes when they exit a smokestack. This relationship laid the foundations for the development of all air dispersion models and formed the basis for the work undertaken by Pasquill to further develop the Gaussian plume equation, which underpinned the development of modern plume dispersion models.

2.2. Gaussian plume models

The first truly recognisable air dispersion model was the Industrial Source Complex (ISC) model developed in the late 1960’s to early 1970’s by the United States Environmental Protection Agency (US EPA). This was the first model capable of considering multiple source types and the interactions between emissions from different sources. The driver for the development of this model was the increasing availability and capability of computing power, allowing far more complex calculations to be undertaken in a reasonable time period. This model was updated and refined over several decades following its release until it was superseded by the adoption and promulgation by US EPA of the AERMOD model in 2005. The ISC model served as a dispersion model for impact assessment projects in Australia until well into the late 1990’s and early 2000’s, often being used in parallel or instead of the AUSPLUME model, which was not considered as reliable as the ISC model for certain applications (such as for particulate modelling in coal mine