Sarajevo: https://duckduckgo.com/?q=sarajevo+winter+smog&t=ffab&iar=im...

Skopje: https://duckduckgo.com/?q=skoplje+winter+smog&t=ffab&iar=ima...

Keep in mind that both of these are in the valley surrounded by hills and mountains, forcing the smog to stay for days during colder weather with no rain or snow to disperse it.

On top of that, there's a report published this month that estimates about 19k deaths across Europe in the past three years because of coal-powered power plants in the WB6 area: https://www.euronews.com/2021/09/07/western-balkan-power-pla...