A documentary by a former state media investigative journalist about the dangerous health impact of China's smog has gone viral on the Chinese Internet, just days before the country hosts top level meetings in Beijing.

Chai Jing's gripping, nearly two-hour investigative documentary begins with her standing on a dimly lit stage in jeans and a white blouse, talking about one of the worst bouts of smog Beijing has seen in recent years, during the winter of 2013. That winter was when she learned she was pregnant.

"This was the PM 2.5 curve for Beijing in January 2013, when there were 25 days of smog in one month," Chai says.

Behind her is a large graph of that month's measurements for PM 2.5, tiny particles in the air that are absorbed by the lungs and blamed as a cause of heart and lung disease.

Chai says the birth of her daughter, and the fact she was born with a benign tumor that had to be removed quickly after birth, prompted her to learn more. She wanted to answer three basic questions for her child: What is smog? Where does it come from? What can we do about it?

She is not alone in her concern about China's massive pollution problem, more than 100 million people online have watched her documentary "Under the Dome."

Surprisingly for China, a country that heavily censors online activity, the video and commentary continues to spread, and the country's newly-appointed Environmental Minister Chen Jining has even praised the video.