Abstract: To effectively identify vessels using fuel with excessive sulfur content,a reverse calculation method for determining fuel sulfur content was developed based on emission and diffusion characteristics. A Gaussian puff compensation model was applied to estimate the emission source strength of vessels from monitored SO₂ concentrations at designated points. In addition,a computational model for vessel fuel consumption was established using key vessel parameters,including the power and fuel consumption rates of main and auxiliary engines. The proposed method demonstrated superior performance compared to the mainstream carbon balance method in detecting vessels with noncompliant sulfur content,achieving detection and false detection rates of 86. 60% and 2. 06%,respectively. Over a 30-day continuous monitoring period,the fuel sulfur content of 2,743 vessels was successfully determined,representing an effective detection rate of 82. 72%. Among these,131 vessels were identified as potentially exceeding sulfur limits.Subsequent verification confirmed that 111 vessels used non-compliant fuel,resulting in an assessment accuracy of84. 73%. These findings demonstrate the method’s capability to enable real-time monitoring of fuel sulfur content without requiring CO₂ concentration data.