Which is interesting, as either air quality does not matter that much or those data are just bogus.
Well, air quality matters probably, so we are left with the data. Let's check what is the origin of this information: https://www.iqair.com/poland/lesser-poland-voivodeship/krako...
6 stations. One from "corporate contributor" named Arek (common Polish first name, short from Arkadiusz so does not look like a big corp) plus 5 other individual contributors.
What equipment those 6 stations have? No idea. Are the instruments calibrated properly? No idea. Are they placed in the right spot, not on the balcony near the chimney? No idea. Are they placed evenly across Krakow to give reliable city-wide data? Looking on the provided locations - not really.
Iqair seems to "crowdsource" their measurements so they get "crowdsourced" data, which can be total crap. Do they even verify those data? How? No idea.