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,

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.