Black snow has been blanketing a city in Kazakhstan, leaving residents worried by the coal coloured flakes.
Officials in Temirtau said they were investigating as locals blamed emissions from the city's numerous factories for the phenomenon.
Some of them told The Astana Times that there was a strange smell wafting around the city.
Environmental experts, prosecutors and city representatives have come together to investigate. They were joined by officials from the central Karaganda region where the city is based.
Many residents have blamed the country's biggest steel production plant - Karaganda Metallurgical Combine - which is based in the city that is home to Kazakhstan's iron industry.
Alibek Bekmukhametov, who head's the a region's Ecology Department told local media that the plant exceeded the legal emissions limits.
It is owned by ArcelorMittal Temirtau, a subsidiary of the global industrial giant ArcelorMittal.
The Independent has reached out to the company for comment, but none had arrived at the time of publication.
Temirtau is considered the worst city in the country for harmful emissions.
In December 2017, Kazakhstan's meteorological agency recorded levels of hydrogen sulphide in the city, which exceeded the government-mandated limit by more than 11 times.
The previous year, the country's statistics committee found almost 600,000 tons of harmful substances had been released into Karaganda's air.
The plant also failed to meet general environmental protection standards, Mr Bekmukhametov said, noting that the company would be fined a total of 150m tenge (£3.3m) for the breaches.
The company told local media it had pledged $56.4m (£49.4m) to improve its cleaning equipment.
