MARCH 1, 2015 5:13 AM March 1, 2015 5:13 am
 
Chai Jing said she was prompted to make her documentary, “Under the Dome,” by concern over the threats pollution posed to her daughter’s health.
 
Updated, 7:48 p.m. ET| 
 
Millions of Chinese, riveted and outraged, watched a 104-minute documentary video over the weekend that begins with a slight woman in jeans and a white blouse walking on to a stage dimly lit in blue. As an audience looks on somberly, the woman, Chai Jing, displays a graph of brown-red peaks with occasional troughs.
 
“This was the PM 2.5 curve for Beijing in January 2013, when there were 25 days of smog in that one month,” explains Ms. Chai, a former Chinese television reporter, referring to a widely used gauge of air pollution. Back then, she says, she paid little attention to the smog engulfing much of China and affecting 600 million people, even as her work took her to places where the air was acrid with fumes and dust.
 
“But,” Ms. Chai says with a pause, “when I returned to Beijing, I learned that I was pregnant.”
 
She has said her concerns about what the filthy air would mean for her infant daughter’s health prompted her to produce the documentary, “Under the Dome.” It was published online Saturday, and swiftly inspired an unusually passionate eruption of public and mass media discussion.
 
“I’d never felt afraid of pollution before, and never wore a mask no matter where,” Ms. Chai, 39, says in the video. “But when you carry a life in you, what she breathes, eats and drinks are all your responsibility, and then you feel the fear.”
 
By early Monday morning, “Under the Dome” had been played more than 20 million times on Youku, a popular video-sharing site, and it was also being viewed widely on other sites.
 
Tens of thousands of viewers posted comments about the video, many of them parents who identified with Ms. Chai’s concern for her daughter. Some praised her for forthrightly condemning the industrial interests, energy conglomerates and bureaucratic hurdles that she says have obstructed stronger action against pollution. Others lamented that she was able to do so only after leaving her job with the state-run China Central Television.
 
“Support Chai Jing or those like her who stand up like this to speak the truth,” said one of the comments — which exceeded 25,000 by Sunday afternoon — on Youku. “In this messed-up country that’s devoid of law, cold-hearted, numb and arrogant, they’re like an eye-grabbing sign that shocks the soul.”
 
The documentary is part science lecture, part investigative exposé and part memoir, and Ms. Chai’s own story has become a focus of praise and criticism. Ms. Chai and her husband were wealthy and privileged enough for her to have given birth in the United States, according to a flurry of news reports last year, and some comments accused her of hypocrisy. Her daughter was born with a benign tumor that required surgery; newspapers have quoted scientists who have challenged Ms. Chai’s suggestion in the video that smog was to blame.
 
But most of the reaction welcomed her initiative in producing and posting the documentary with her own money. Indeed, some have wondered how Ms. Chai got away with it.