Abstract
<jats:p>This study examines environmental protection during sea passages in the coastal waters of Northern Europe, focusing on nitrogen oxides (NOx) from marine diesel exhaust as a primary source of uncontrolled air pollution, especially hazardous in high-humidity regions. In response, MARPOL designates special emission control areas that impose stricter NOx limits. We evaluate exhaust gas recirculation (EGR) as a principal, widely used measure to meet these limits during operations within such areas. Experiments were conducted on a 65,000-DWT general cargo vessel trading in Northern European special areas. The ship was fitted with a combined EGR arrangement incorporating both high- and low-pressure loops. We propose assessing EGR effectiveness—and, by extension, the environmental friendliness of passages—in terms of an environmental sustainability index referenced to NOx emissions. Results show that the integrated EGR system enabled the vessel to meet MARPOL NOx requirements across test conditions. The most effective operating modes corresponded to the highest practicable recirculation rates of both loops. Under these conditions, the environmental sustainability index reached 30.00–35.88%, representing the maximum measured reduction potential within the study. These findings support complex EGR control as a viable pathway for compliant, lower-impact operations in Northern European coastal waters.</jats:p>