Exhausts from ships are an important source of air pollution in coastal regions. We observed a ~ 3 fold reduction in the level of sulfur dioxide (a principle pollutant) from the English Channel from 2014 to 2015 after the new International Maritime Organisation regulation on ship sulfur emission became law. Our estimated ship's fuel sulfur content shows a high degree of compliance. Dimethylsulfide from the marine biota becomes a relatively more important source of sulfur in coastal marine air.