Residents of Russian city protest 'black sky' air pollution Residents of a city in Russia's Ural Mountains are expressing worry over industrial pollution after heavy smog enveloped Chelyabinsk this month and remained for two weeks

CHELYABINSK, Russia -- Residents of a city in Russia's Ural Mountains are expressing worry over industrial pollution after heavy smog enveloped Chelyabinsk this month and remained for two weeks.

Low winds helped the thick grey layer of smog, what locals are calling "black sky," settle over the city of 1.2 million. The Chelyabinsk meteorological office reported that air pollution exceeded permissible levels before the smog dissipated.

On Sunday, about 700 protesters braved temperatures of -20 degrees Celsius (-4 degrees Fahrenheit) to demand cleaner air. They held banners reading "We want clean skies!" and "Stop poisoning our children!"

The protest followed up on an earlier one in which participants tried to force their way into the mayor's office.