The Baltic Sea's designation as a sulfur emission control area in 2006, with subsequent regulations, significantly reduced sulfur emissions from shipping. Our study analysed air quality data from 2003 to 2020 on the island Utö and employed modelling, showing a continuous decrease in SO₂ concentrations since 2003 and thus evidencing the effectiveness of such regulations in improving air quality. It also underscored the importance of long-term, high-resolution monitoring at remote marine sites.