Air pollution in Sofia, like in many Bulgarian cities such as Pernik, Burgas, Plovdiv, and Ruse, is a problem that goes way back. In recent years, several studies by the European Environment Agency have consistently placed Bulgaria at the top of the unflattering ranking of countries with the worst air quality, while Sofia has repeatedly earned the title of most polluted EU capital.
There are various factors that make Sofia so vulnerable to air pollution.
On the one hand, there is city traffic: in Sofia, a city now inhabited by over 1,2000,000 people, there are now 550-600 cars per 1,000 inhabitants. A not only huge, but old fleet of cars, largely comprised of polluting diesel engines.
Another cause of pollution is related to the heating systems of houses and apartments.
According to data from the National Program for the Improvement of Air Quality, in Sofia over 10% of the population in winter uses solid fuels. [Source: OBC Transeuropa]