## 3 Result and Discussion
### CO Emission According to Vessel's Operation  
To evaluate CO emissions from diesel engines mounted on ships, exhaust gases from two large passenger ships, two small passenger ships, and one fishing boat sailing along the coast were measured during operations using a PEMS. Figure 5 shows the real-time CO emission measurement results according to rpm variations for five experimental ships in normal operation modes. With increasing rpm, the load on the engine increases; this causes the fuel consumption to increase, and the CO emission (unit: g) also increases as shown in graphs (a)-(e) of Figure 5. In addition, the data show that CO emissions change with rpm when the rpm of each ship changes, as shown in graphs (a) and (e) of Figure 5. In particular, CO emissions react sensitively to instantaneous rpm fluctuations at a low rpm. Figure 4: Pearson correlation result. Overall, higher rpm values correlate with higher CO\({}_{2}\) emissions; CO\({}_{2}\) emissions at the highest rpm vary depending on the type and capacity of the engine used. This is because the fuel consumption required at the maximum output is different depending on the engine capacity (unit: cc). In international trade ports such as Shanghai, Busan, and Singapore, CO\({}_{2}\) emissions are expected to be higher than in other regions because large ships with relatively large capacity engines frequently stop at these ports. In particular, when applying a carbon tax policy to shipping companies, the size of the engine mounted on the ship should be used as a standard. The rpm of a ship fluctuates depending on external influences, such as current and wind direction, and there is a difference in fuel consumption required by the engine to maintain the rpm and speed. As shown in part (a) of Figure 5, there is a difference in CO\({}_{2}\) emissions even in 140 rpm conditions, and it is assumed that this has an influence on the external environments. Since the current and wind direction change depending on the season, it is necessary to evaluate the impact on the external environment according to the season during which CO\({}_{2}\) emissions in the shipping sector are evaluated. [PERSON] et al., [PERSON] et al., and [PERSON] et al. evaluated the seasonal impact on air pollution emissions from ships [24; 25; 26], and when considered together with the results of this study, the development of optimal sailing routes for each season is considered essential to minimize greenhouse gas emissions. [PERSON] et al. (2010) demonstrated that engine load (speed) and fuel consumption have a linear relationship; consequently, CO\({}_{2}\) emissions were also related [27]. Therefore, to reduce CO\({}_{2}\) emissions in port areas close to land, it is necessary to improve dock facilities to make it easier to dock and develop a docking method that is most suitable for the dock environment using navigation simulations; this can reduce CO\({}_{2}\) in the long term. Generally, the emission factor used to calculate CO\({}_{2}\) emissions is fuel-based (kg-CO\({}_{2}\)/tonne-fuel) or power-based (kg-CO\({}_{2}\)/kWh). However, it is difficult to measure data on real-time fuel consumption or engine output on vessels other than commercial ships, and collecting data is even more difficult. Each ship's engine has a different maximum rpm and CO\({}_{2}\) emissions depending on the capacity of each engine. Therefore, in order to understand the effect of the fuel consumption on the environment, we need to understand the effect of the fuel consumption on the environment. Figure 5: CO\({}_{2}\) emission by rpm variance. (**a**) SSD 1; (**b**) SSD2; (**c**) HSD 1; (**d**) HSD 2; (**e**) HSD. to achieve standardization, the rpm measured from SSD 1 to HSD 3 is converted into a dimensionless number as shown in Equation (3), and the dimension is reduced by using the Log function for CO\({}_{2}\) emissions in g units.