50 1 Introduction 
31 Air pollution contributes to increased morbidity and mortality in humans (Cohen et al., 
52 2017). Pollutant sources such as power plants, waste incineration, buildings construction and 
53 transport cause large quantities of pollutants to be exhausted to the environment. For human 
54 exposure, transport — primarily including road and sea transport — is often the main source in urban 
35 environments (EEA, 2021). 
56 Maritime atmospheric pollution affects coastal areas and ports by causing human health 
37 issues and degrading climate and atmospheric composition (Eyring et al., 2010). Emissions from 
58 shipping in 2018 corresponded to 2.89% of total greenhouse gases (IMO, 2020) while the 
59 corresponding contribution to SOx and NOx emissions is estimated at 5-9% and 15%, respectively 
50 (Corbett et al., 2007; Eyring et al., 2010). The contribution to particulate emissions varies between 
51 1-14% for PM2.5 and 1.7% for PM1O, in busy European coastal areas (Viana et al., 2014). 
Air pollutant emission restrictions and regulations have for years been applied to road 
transport emissions to improve air quality, but the maritime sector only recently received proper 
attention. The International Maritime Organization (IMO) is responsible for setting new rules for 
the reduction of pollutants emissions. Ship operators must follow these regulations, while 
governmental authorities are responsible for monitoring compliance. One remarkable change in 
the regulation was implemented on January 1“, 2020, with the maximum permissible fuel sulphur 
content (FSC) not exceeding 0.50% S m/m globally, following up on the earlier introduction of 
0.10% S m/m in emission control areas (ECAs) (IMO, 2016). Prior to 2020 and 2015, the limits 
were at 3.5 and 1.0% S m/m, respectively. As an alternative to using low sulphur fuel, ships are 
allowed to operate with exhaust gas cleaning systems (scrubbers) to meet an equivalent quantity 
of SOx emissions, similar to the use of low sulphur fuel. 
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The court-approved monitoring of compliance with the limit values according to MARPOL 
Annex VI (EU, 2016) is carried out in the ports by random checks on board the vessels by 
government inspectors. With the implementing decision 2015/253/EC (EU, 2015), the EU 
Commission has defined the frequency of inspections and fuel sampling on board. This EU 
directive also states that the sampling frequency in a country can be reduced, at most halved, if the 
country uses remote plume measurements to preselect vessels for on board inspections (risk- based 
assessment). Therefore, in some countries like Germany, Sweden, Denmark or Finland, authorities 
install air measurement stations in specific coastal areas. In these, analytical devices are used to 
collect both ship plume and background concentration data and, from these, to identify the 
chemical composition of the plume and therefrom calculate the sulphur content of the currently 
burned fuel (Kattner et al.. 2015). 
84 However, several difficulties exist in such an approach, primarily due to the often-low 
35 concentrated pollutants in highly diluted plumes from vessels that approach the measuring station 
36 only from a distance of several hundred meters (MFVM, 2018). Plume dispersion modelling to 
37 assess the impact of shipping in port areas is commonly studied by simulating ships as point 
38 sources, using lagrangian gaussian puff models, such as CALPUFF (Lonati et al., 2010; Murena 
89  etal., 2018). Bali et al. (2020) used CALPUFF model to produce time-series of single ships passing