## 2 Site Description and Techniques for Data Analyses
### Numerical Modelling
#### 2.4.2 Models Description and Set-Up
A meteorological pre-processor calculates the required boundary layer parameters from a variety of input data (in our case data were provided by a meteorological station). One of the main advantages of the ADMS-Urban model over other dispersion models is that the boundary layer structure is based on two parameters: the Monin-Obukhov length and boundary layer height, instead of a single Pasquill-Gifford parameter. Model is time independent so there are no time steps; there are no limits to horizontal and vertical spatial resolution. No numerical methods are required except Runge Kutta for plume rise model and adaptive time stepping for chemistry. As for the chemistry, ADMS-Urban models NOx chem  
Figure 2: **(a)** BOLCHEM parent domain (in blue) and nested domain (in green); **(b)** ADMS domain with indication of the subdivision of the port into four areas (areas 1, 2, 3: hotelling areas). istry using the 8 reaction Generic Reaction Set [55]. This scheme is a semi-empirical photochemical model which reduces the complicated series of chemical reactions involving NO\({}_{X}\), NO\({}_{2}\), and O\({}_{3}\) and many hydrocarbons to 8 reactions. It is employed in the following manner. Firstly, dispersion of NO\({}_{X}\), NO\({}_{2}\), and O\({}_{3}\) and VOC pollutants is calculated. Hourly background concentrations (in this case obtained from BOLCHEM) are then added onto these calculated concentrations. Finally, an adaptive time stepping technique is used to model the chemical reactions. Further details can be found at [[https://www.cerc.co.uk/environmental-software/assets/data/doc_techspec/P18_03.pdf](https://www.cerc.co.uk/environmental-software/assets/data/doc_techspec/P18_03.pdf)]([https://www.cerc.co.uk/environmental-software/assets/data/doc_techspec/P18_03.pdf](https://www.cerc.co.uk/environmental-software/assets/data/doc_techspec/P18_03.pdf)) (accessed on 1 March 2021). PM is only dispersed, and the final concentrations obtained from ADMS-Urban does not include secondary aerosols as consequence of ship emissions. The model is continually validated against available measured data obtained from real world situations, field campaigns and wind tunnel experiments. It has been validated using many experimental datasets that test different aspects of the models, for instance: ground/high level sources, passive and buoyant releases, buildings, complex terrain, chemistry, deposition, and plume visibility. These studies are both short-term as well as annual, and involve tracer gases or specific pollutants of interest (a review of studies is available at: [[http://cerc.co.uk/environmental-software/model-validation.html](http://cerc.co.uk/environmental-software/model-validation.html)]([http://cerc.co.uk/environmental-software/model-validation.html](http://cerc.co.uk/environmental-software/model-validation.html)) (accessed on 1 March 2021)). In this study, the input data used to run ADMS-Urban were sources parameters, source emissions, hourly meteorological data obtained from the 10 m high meteorological station located close to the study site, the surface roughness z\({}_{0}\) for both the study area (equal to 0.75 m being this an urban area) and for the meteorological site (equal to 0.5 m being a suburban area), and the latitude (40.38\({}^{\circ}\)). Only ship-related emissions were explicitly reproduced for the same period of the measurement campaign. The port was split into three hotelling areas and one manoeuvring area. Each ship was assigned and randomly positioned in the area containing its own quay and to the manoeuvring area (Figure 2b).