Cargo ships are unregulated and burn the lowest grade oil called bunker fuel. These ships can emit the equivalent sulfur emissions of 19 million ICE vehicles.[1] [1] https://www.cadmatic.com/resource/articles/does-one-ship-pol...
Not as of January 01 - there's a new regulation this year that imposes a sulfur cap on fuel burned by cargo ships [1]. Most ships must now burn more expensive and cleaner fuels. Some ships - mostly larger ones - still burn HSFO but they can only do so because they've installed "scrubbers" which clean the emissions to reduce the amount of sulfur emitted into the atmosphere.
It's an open question whether scrubbers are really helping or just a diversion from purchasing higher quality fuel, but it's only economical to install scrubbers on the very big ships and so the large majority of the ~50,000 strong merchant marine fleet don't have them installed.