And shipping is the most egregiously polluting transportation in existence. Something like 10 to 30% of emissions come from 6000 ships in service. Folks claim its ok because it settles into the ocean quickly - ok for everybody but the ocean.
Some 10% to 30% of sulfur emissions come from those ships. They do that because they move in the open ocean where nobody cares about a short lived pollutant.
Sulfur moves quickly into the ocean where it not only non-toxic, but also beneficial to life. (Sulfates - what it will settle down into - is widely used as fertilizer on land.)