I think the Sulphur and NOx emissions are that high because ocean ships are using lower grade fuel with lots of Sulphur (many times more than regular Diesel fue

I think the Sulphur and NOx emissions are that high because ocean ships are using lower grade fuel with lots of Sulphur (many times more than regular Diesel fuel) and have no NOx reduction devices like a regular truck. It is possible to reduce Sulphur and NOx emissions an order of magnitude just by making ships EURO 6-equivalent compliant. That would increase the shipping cost a bit, but it will still be the cheapest by far, the $500 per container from Shanghai to LA will go $520 or $550.