Proposal of CO₂e indicator for policies of maritime transportation emissions

The combustion of marine fuels results in emissions of pollutants and diesel exhaust that contains 450 different compounds. Most control policies on substances target non-CO₂ emissions that have tangled linear and non-linear relationships with fuel usage. In addition, some of the controls on pollutants have uncertain or positive effects on global warming. A holistic approach should be adopted to avoid harming progress in the fight against climate change. This paper discusses a method to assess a CO₂ equivalent indicator for primary shipborne emissions. The aim is to keep climate change and air quality indicators together. A derivative of the CO₂e (Carbon Dioxide Equivalent) model of Global Warming Potential (GWP) has been developed for well-mixed greenhouse gases, near-term climate forcers, and air pollutants. The model has been attained from calculations made on thermopower plants and adapted to ships. Well-to-Wake emissions without transportation emissions are considered to curb the bunkering disadvantages of alternative marine fuels. The proposed indicator shows linearity to the existing metrics and indicates the importance of emission metric choice. Hence, the flexible nature of the indicator allows more comparisons with alternative fuels. The indicator was then applied to marine distillate fuels, heavy fuel oil, and liquefied natural gas. Among them, on a scale of proposed indicator, marine distillate fuels are the most environmentally harmful, whereas liquefied natural gas is the least harmful. As the calorific value of fuels is considered, distillate marine fuel emissions are 0.9% and 16.5% more impactful than heavy fuel oil and liquefied natural gas, respectively.