Review of developments in air quality modelling and air quality dispersion models

Air dispersion models are mathematical tools used for simulating the physical and chemical processes governing the diffusion and transformation of pollutants in the atmosphere. The simplest dispersion models are steady-state Gaussian plume models. They are based on mathematical approximation of the plume behaviour and follow some basic assumptions that may not always present a realistic scenario. Despite having these limitations, they provide reasonable results when used aptly. More recently, advanced dispersion models are being developed, which are based on a more refined approach of simulating the dispersion phenomenon following the properties of the atmosphere rather than relying on general mathematical approximation. This has expanded the field of modelling to tackle difficult situations such as complex terrain and long-distance transport. In this review paper, the developments in air quality modelling, with emphasis on dispersion modelling, are presented. Further, a few models are selected representing different categories in dispersion modelling, which are Gaussian models - American Meteorological Society/Environmental Protection Agency Regulatory Model, Caline4, Airviro Gauss, Complex Terrain Dispersion Model and Fugitive Dust Model; Eulerian models - California Grid Model, Flexible Air Quality Regional Model and Panache; Lagrangian models - Graz Lagrangian Model, Flexible Particle Dispersion Model, Austal2000 and Hybrid Single Particle Lagrangian Integrated Trajectory Model; and advanced dispersion models - UK-Atmospheric Dispersion Modelling System 5, The Air Pollution Model and Calpuff. A comparison has been done based on certain characteristic features obtained from various publications.