Russian police have opened a criminal case into air pollution in the Siberian coal-mining region of Kemerovo, weeks after black snow first covered towns in the area.

Dark snow descended on the cities of Prokopyevsk, Kiselyovsk and Leninsk-Kuznetsky in mid-February, a phenomenon that has been attributed to rising coal output. Authorities in another Kemerovo town were reprimanded in December for using white paint to cover up ash- and soot-covered snow.

The regional police department announced Monday that it had opened a criminal case into air pollution against an unnamed factory after a complaint filed by a resident of Kiselyovsk. The charges carry a fine of up to 80,000 rubles ($1,226) and suspension from holding office for up to 5 years.

Tests revealed more than double the permissible amount of pollutants in the air, the Kemerovo region Interior Ministry department said.

Here is a selection of photos posted by social media users:

Black snow engulfs cars on the street.