278 
279 
280 
281 
282 
283 
284 
285 
9C (WC) _ 9 (pn .9C\_o 
öt 0x 0x \ IT 0x) 
Zu} 
In Eq. 2, C represents the pollutant concentration and Def is the effective diffusivity, 
which includes both molecular and eddy diffusivity and constitutes the coefficient that 
characterizes trace gas mass transfer in the atmosphere. Molecular diffusivity depends on gas 
properties and in this study, the values for CO2 and SO: are considered to be 0.14 cm”/s and 0.11 
cm”/s, respectively (Massman, 1998). The eddy diffusivity D, is related to atmospheric turbulence 
characteristics and is calculated by the turbulent Schmidt number equation (Eg. 3), where v4 is the 
turbulent viscosity produced by CFD results by assigning the value of 0.7 for the Schmidt number 
(Gualtieri et al., 2017; Tominaga & Stathopoulos, 2007). 
Ve 
Sce = D. 
(3) 
The simulation of turbulence with RANS can be accomplished by different models and the 
SST k-® turbulence model was applied in the present study. This model constitutes a mixture of 
standard k-e and standard k-@ models, which can stand as separate turbulence models. The SST k- 
® hybrid uses the standard k-@ model equations for boundary layer modelling and standard k-& 
model expressions in the free-stream flow cells of the domain. It is assumed that this turbulence 
model can better fit this work’s cases due to its demonstrated efficacy in the study of Toscano et 
al. (2021), where plume dispersion from ships was modelled. 
293 The Atmospheric Boundary Layer (ABL) formulas were used as input boundary 
294 expressions for wind and turbulence conditions at the Side Domain boundaries (Yang et al., 2009). 
295 The wind velocity profile is expressed by Equation 4, where u. is the friction velocity (Eq. 5), x 
296 is the von Karman constant and equals 0.41, z the variable that corresponds to the height from the 
297 bottom surface, Zg is the aerodynamic roughness length that has been set to 0.0002 (Wieringa, 
298 1992), and u, Is the velocity calculated at the reference height Her. 
. + 
HD = (>) 
K ZZ 
(A 
299 
300 
301 
302 
303 
304 
U = Uref K 
Sn Href + Zo 
In (er 7 ) 
x. 
vw J 
na 
Wind data for setting up the CFD model are available in the area and are given by the MS 
(Table 4). Neither wind direction nor speed differs substantially between the five cases. The wind 
direction is adjusted by rotating the vessel model relative to the domain, considering the ship’s 
direction (Table 4), while the wind speed is taken to correspond to the u,2; of Equation 5 at Hyes 
at 9 m above the water level. 
13