Bosnian capital Sarajevo covered by smog

The arrival of winter has shrouded Sarajevo, the capital of Bosnia and Herzegovina, under a blanket of air pollution, according to figures released Tuesday by air quality technology firm IQAir.

The Swiss company's data showed that air pollution in Sarajevo was 171 based on the U.S. Air Quality Index, an indicator used by the U.S. Environmental Protection Agency that denotes greater pollution as the reading goes up. This was also 18.7 times the UN World Health Organization (WHO) annual air quality guideline value.

Known for its historical and natural beauty, the city has become nearly invisible from the high surrounding mountains from the thick smog.

Air pollution in Sarajevo is mainly caused by the exhaust of old-model vehicles, as well as low-calorie fuels used for heating.

It is not the only city in the Western Balkans to suffer from poor air quality. The air pollution level in North Macedonia's capital Skopje is 154, according to IQAir.

Air pollution accounts for a many premature deaths, poor health, and lower educational test scores, according to numerous studies.