What is the largest source of sulfur dioxide air pollution?
Coal burning releases the largest amount of sulphur dioxide air pollution.
This acidic substance dissolves in clouds & makes the rain acidic, which links back to why acidic rain is called 'ACID rain'.
A process of cleaning flue gases of sulphur dioxide after burning coal in power stations, is the spraying of sea water which is naturally alkaline, into the gases to react with the sulphur dioxide, neutralising it's acidity.
This is why oceans could be a major sink for sulphur dioxide currently in our atmosphere.
Hope this helps.