sulphur dioxide vs pollutant

sulphur dioxide and pollutant both are nouns.

Word	Noun	Adjective	Verb	Adverb
sulphur dioxide	Yes	No	No	No
pollutant	Yes	No	No	No

As nouns, pollutant is a hypernym of sulphur dioxide; that is, pollutant is a word with a broader meaning than sulphur dioxide:

sulphur dioxide: a colorless toxic gas (SO2) that occurs in the gases from volcanoes; used in many manufacturing processes and present in industrial emissions; causes acid rain
pollutant: waste matter that contaminates the water or air or soil

Other hypernyms of sulphur dioxide include dioxide, gas.

sulphur dioxide (noun)	pollutant (noun)
a colorless toxic gas (SO2) that occurs in the gases from volcanoes; used in many manufacturing processes and present in industrial emissions; causes acid rain	waste matter that contaminates the water or air or soil