Does it even make sense to look at this on a country level perspective? Countries have different sizes and it heavily depends where you are and also where the air monitor stations are placed.
As an example if Finland had one air quality station in Helsinki and the 10 in the “remote wilderness” for scientific purposes, then the data likely would be skewed.
Usually when considering safe air you'd take into account population density. The goal is to find a number that represents how many inhabitants are affected by pollution after all.
E.g. you weigh air measurement stations by the surrounding population density.
As an example if Finland had one air quality station in Helsinki and the 10 in the “remote wilderness” for scientific purposes, then the data likely would be skewed.