NBC: As Chinese President Xi Jinping joined world leaders for the U.N. climate change summit, millions in his homeland were choking on the most severe air pollution of the year.
The air-quality index soared past 700 -- well above the hazardous level -- in Baoding on Monday.
Located about 90 miles south of Beijing, Baoding's 11 million residents struggled to see through the thick haze of smog. Poor conditions were also reported in other parts of northern China, including the capital.
"Most days...