Characterizing the vertical concentration profiles of ship plumes with a microscale model - is it all Gaussian?

Accurate modeling of ship emissions is a topic of increasing interest due to the ever-growing global fleet and its emission of air pollutants. With the increasing calculation power of modern computers, numerical grid models can nowadays be used to analyze effects of shipping emissions from global to local scales. However, modeling entire ports and larger domains still requires a good representation for the vertical concentration profile of single ship plumes. As the shape of the plume strongly varies depending on parameters like plume temperature, ship-induced turbulence and meteorological conditions, the plume dilution does not always appear to be represented by a simple Gaussian distribution. In this work, the microscale model MITRAS is used to calculate vertical concentration profiles of ship plumes under varying technical and meteorological scenarios. The resulting curves are fitted with different mathematical curves (e.g. Gaussian, Polynomial and Gamma distribution) by a least square minimization approach and the best representations for individual scenarios are discussed.