As delegations from governments around the world gather in Paris to push for a deal to battle climate change, the capital of the world’s biggest polluter has issued a “red alert” over severe smog.

Starting Tuesday and continuing for three days, the more than 20 million residents of Beijing will have heavy limitations imposed on their daily activities. Schools will be closed, outdoor construction will be halted, and as the BBC reported, “cars with odd and even number plates will be banned from driving on alternate days.” It’s the first time China’s highest alert has ever been enacted in the city.

This latest development in China’s ongoing air-pocalypse comes after smog levels reached a 13-month high last week. To exhibit the extent of the haze, some residents posted outlines of famous buildings that were otherwise obscured by the pollution. As above, here’s the Temple of Heaven again:

Wu Jie News

At that time, the Chinese government issued an orange alert, the second-highest level in the country’s four-tier warning system. “Air pollution monitors showed that areas of Beijing had more than 256 micrograms per cubic meter of poisonous particles,” notes The Independent. “The World Health Organization (WHO) says that anything over 25 micrograms is considered unsafe.”

Citing a study conducted earlier this year, The Wall Street Journal noted that “air pollution could prematurely kill more than 250,000 Chinese residents in major cities.” In some parts of Beijing, visibility has been limited to less than 700 feet.