Pollution of the air can occur from the exhaust emissions from a ship's engine. The most harmful emissions are nitrogen and sulphur chemicals which result from burning ship's bunker oil. International regulations require ship's engines to be designed to minimise nitrogen emissions.
Sulphur emissions depend on the amount of sulphur in the bunker fuel being used. There is a world wide regulation that limits the amount of sulphur in bunker fuel. In places like Europe where there are many ships, there are areas where ships can only use bunker fuel with a very low amount of sulphur.
Sulphur and nitrogen chemicals in the air can have a harmful effect on plants and marine animals and can cause breathing problems in people.
The production of greenhouse gases by ships is slowly being addressed. Until international regulations can be agreed the shipping industry is taking a number of voluntary steps: