The black snow that fell in the Siberian city of Omsk last week was ash, the Federal Service for Natural Resources Use has said.
The chemical makeup of snow samples sent to the agency was characteristic of ash formed from coal combustion, Interfax reported Monday, citing silicon oxide, aluminum oxide, iron oxide and calcium oxide as the ash's main components.
It still has not been determined who was responsible for the ash emissions, which were reported in Omsk on Dec. 11 and 14. Although local coal producer Omsktekhuglerod was initially thought to be the pollutant, experts have since said that it is unlikely that the factory is to blame.
The Federal Service for Natural Resources Use is continuing its check into Omsktekhuglerod, however, as well as Thermal Power Station No. 5, which belongs to Territorial Generation Company No. 11.
The agency did not say whether the ash was harmful to the health of humans and animals.