Air quality in Beijing and elsewhere in China has been deemed unsafe for years. In 2013, Edward Wong, a New York Times correspondent, detailed the health risks he, his wife and their young daughter faced by living in a “toxic country.”

I want my daughter to grow up appreciating the outdoors — sunsets and birdcalls and the smell of grass or the shape of clouds. That will be impossible if we live for many more years in Beijing. Even with my adult-size lungs, I limit my time outdoors

As bad as the air quality is in China, a report this year claimed that readings in Xi’an, the provincial capital of Shaanxi, had been falsified: Cotton stuffed into equipment at air-monitoring stations delivered cleaner readings.