Black snow blanketed Temirtau in Kazakhstan, leaving the city's residents worried by coal-colored flakes.
Residents told The Astana Times of a strange smell wafting around the city and blamed the emissions on the city's factories.
Temirtau officials said they would investigate. Environmental experts, prosecutors and city representatives were joined by officials from the central Karaganda region where the city is based.
Many suspected the country's biggest steel production plant, Karaganda Metallurgical Combine, the home of Kazakhstan's steel industry.
Based in the city, Karaganda Metallurgical Combine is owned by ArcelorMittal Temirtau, a subsidiary of the global industrial giant ArcelorMittal.
The plant exceeded legal emissions limits, regional environmental chief Alibek Bekmukhametov told local media.
Temirtau is considered the worst city in the country for harmful emissions.
In December 2017, Kazakhstan's meteorological agency recorded levels of hydrogen sulfide in the city that exceeded the government-mandated limit more than 11 times.
The previous year, the country's statistics committee found almost 600,000 tons of harmful substances in Karaganda's air. (Compiled by Qiaowai)