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Environment

The geographic position of the Sofia Valley limits the flow of air masses, increasing the chances of air pollution by particulate matter and nitrogen oxide. Solid fuel used for heating and motor vehicle traffic are significant sources of pollutants. Smog thus persists over the city as temperature inversions and the mountains surrounding the city prevent the circulation of air masses. As a result, air pollution levels in Sofia are some of the highest in Europe.

Particulate matter concentrations are consistently above the norm. During the October 2017 – March 2018 heating season, particulate levels exceeded the norm on 70 occasions; on 7 January 2018, PM10 levels reached 632 μg/m, some twelve times the EU norm of 50 μg/m. Even areas with few sources of air pollution, like Gorna Banya, had PM2.5 and PM10 levels above safe thresholds. In response to hazardous spikes in air pollution, the Municipal Council implemented a variety of measures in January 2018, like more frequent washing of streets. However, a report by the European Court of Auditors issued in September 2018 revealed that Sofia has not drafted any projects to reduce air pollution from heating. The report also noted that no industrial pollution monitoring stations operate in Sofia, even though industrial facilities are active in the city. A monitoring station on Eagles' Bridge, where some of the highest particulate matter values were measured, was moved away from the location and has measured sharply lower values since then. Particulates are now largely measured by a network of 300 sensors maintained by volunteers since 2017. The European Commission has taken Bulgaria to court over its failure to curb air pollution.