Air-quality monitors in Moscow have warned of high-levels of hydrogen sulfide spreading across the city's southeast.
Hydrogen sulfide levels were recorded at levels 2.5 times higher than the government's accepted safety limits in the city's Kapotnya district on Monday morning, Moscow's environmental monitoring agency reported.
Abnormally high levels were also detected in the Lublin and Vykhino-Zhulebino areas, the Interfax news agency reported.
Hydrogen sulfide, which gives off a smell similar to rotting eggs, is found in natural gas. In more populated areas, it is usually emitted by waste water treatment facilities, landfills and farms.
The gas is not expected to cause any adverse health effects.