## 1 Introduction  
Fossil fuels have been widely used for industrial and technological development so the earth is currently facing a serious environmental crisis and ecosystem destruction due to greenhouse gases generated through their use [1]. Recently, interest in greenhouse gas emissions by ships has increased and many policies and regulations are being implemented and studies are being conducted to reduce these emissions and those from various industries [2, 3]. Technologies such as E-fuel and ammonia fuel have emerged as strategies to reduce the dependence on greenhouse gases, but innovative technologies for their commercialization have not yet been developed. In the transportation sector, the main sources of greenhouse gas emissions are passenger cars (41%), medium and heavy trucks (22%), shipping (11%), aviation (8%), and other modes of transport (18%). Most CO\({}_{2}\) is emitted by road mobile sources, such as passenger cars and trucks, whereas ships emit the most CO\({}_{2}\) in the field of nonroad mobile sources [4]. According to a recent IMO study, greenhouse gas emissions from ships, including CO\({}_{2}\), CH\({}_{4}\), and N\({}_{2}\)O, increased by approximately 9.3% from 977 million tons in 2012 to 1076 million tons in 2018, of which around 1056 million tons were accounted for by CO\({}_{2}\)[5]. CO\({}_{2}\) emissions of ships are expected to decrease during 2020-2022 due to the recent decrease in international trade throughout COVID-19. However, as international trade has become active again post-COVID-19, CO\({}_{2}\) emissions from ships are also expected to increase. There are both economic and time limitations when calculating total emissions by measuring air pollutants for a ship during operation; consequently, a method for calculating total emissions using ship activity data and an emission factor was used. Therefore, it is essential to ensure the reliability of the emission factor. Two types of emission factors were used to calculate the contents of air pollutants from ships: fuel- and power-based, whereby the fuel-based emission factor is constant regardless of the engine's operating mode, whereas the power-based emission factor applies different emission factors depending on the engine modes used [6]. Most studies focus on calculating total or regional CO\({}_{2}\) emissions using existing emission factors (fuel-based or power-based) suggested by EEA, IMO, etc. [PERSON] et al. evaluated the relative impact on CO\({}_{2}\) emissions by ship types and sizes using fuel-based emission coefficients [7]. [PERSON] calculated the greenhouse gas emissions generated by ships at four ports in Georgia using ship activity data and emission factors. It was confirmed that greenhouse gas emissions differed depending on the type and size of ships considered. Accurate information concerning activity data, such as ship engine information, is necessary to minimize the uncertainty inherent to the emissions calculations [8]. Unlike previous studies, this study measured CO\({}_{2}\) emissions from actual operating ships using a portable emission measurement system (PEMS, Semtech DS+, Sensors Inc., Saline, MI, USA and Horiba Ltd., Horiba OBS-one, Horiba, Kyoto, Japan) used to measure air pollutant emissions from road mobile sources, such as passenger cars and trucks. A few studies used PEMS to measure air pollutants from ships. [PERSON] et al. compared measurement emission data using a SEMTECH-DS gaseous pollutant analyzer with emission data based on the Automatic Identification System (AIS) [9]. [PERSON] et al. quantified fuel-based emission factors for cargo ships using a PEMS consisting of HORIBA OBS-2200 [10]. In this study, air pollutant emissions from two ocean-going vessels and three coastal vessels were measured using PEMS and compared. The CO\({}_{2}\) emission characteristics of slow-speed and high-speed engines were compared, and fuel-based emission factors were derived and compared with other studies.