This is a real issue throughout europe, particularity in east europe, where germany has been dumping highly polluting cars for decades sometimes even by threatening countries that tried blocking it, as is always the case with german eu politics, using the might of eu fines and sanctions.
That map specifically talks of urban air quality. Foreign visitors hanging out among “beautiful nature” are, well, out in nature, not dense urban environments. Especially in the summer when the lowlands are baking, it is popular for foreign remote workers to head up to mountain resort towns that don’t have a lot of air pollution because they don’t have a lot of cars in the area.
Especially compared to some more remote areas in Western Europe like the Alps or the Massif Central in France. Which would suggest that emissions from cars are not the main reasons why the Balkans (and Eastern Europe is general) are doing so bad.
Air pollution in rural areas in the Western Balkans is, besides vehicles, largely a function of burning wood for heating. For example, look at Korçë in Albania, which is a black spot on your linked map (very high pollution): this surely reflects in part the burning of wood in November–April by nearly the entire town, because it is cold at 800 m, but they do not have access to gas heating, and electric heating is expensive. Again, because the trend is mainly to go up to the mountains in the summer months, when the locals are not running their wood stoves, foreign remote workers avoid the worst of that.
PM10 is basically woodburning stoves. PM2.5 is much more hazardous to your health, and produced by industrial processes to a greater degree. Using PM10 is just artificially tipping the scale to make less-industrialized locations look worse.
Also very high pollutions levels:
https://www.researchgate.net/profile/Jan-Horalek/publication...