pollution vs dirtying

pollution and dirtying both are nouns.

Word	Noun	Adjective	Verb	Adverb
pollution	Yes	No	No	No
dirtying	Yes	No	No	No

As nouns, dirtying is a hypernym of pollution; that is, dirtying is a word with a broader meaning than pollution:

pollution: the act of contaminating or polluting; including (either intentionally or accidentally) unwanted substances or factors
dirtying: the act of soiling something

Other hypernyms of pollution include soiling, soilure.

pollution (noun)	dirtying (noun)
the act of contaminating or polluting; including (either intentionally or accidentally) unwanted substances or factors	the act of soiling something
undesirable state of the natural environment being contaminated with harmful substances as a consequence of human activities
the state of being polluted