Teenager Li Xinwei loves to play badminton, but she has not used the courts in her residential estate for a long time.
"Even though they are indoors, the air quality is bad," the 14-year-old told The Straits Times in between badminton practice sessions at her school. "So I'm glad I can exercise here."
She now plays three times a week, thanks to an inflatable dome set up at Beijing Huijia Private School.
Three storeys high, the 3,000 sq m dome filters out harmful PM2.5 particles and keeps polluted air out by maintaining a higher air pressure inside.
The school has a committee that monitors the air quality index (AQI) for its four domes, and they have been shown to work, according to Huijia's marketing manager, Ms Li Qing.
"The AQI in the dome is always below 30, even if the air is hazardous outside," she noted. An AQI reading below 50 is deemed healthy.
SELLING POINT FOR ELITE SCHOOLS
It's certainly one factor I considered when I enrolled my son in Huijia last year.''
MS YANG WEI, a Beijing mother who wants her child to enjoy clean air growing up
In fact, when Beijing issued its first pollution red alert last month, Huijia - which also runs Singapore international school Hillside World Academy - moved its 800 primary school pupils into the biggest dome for classes.
The domes, which are made from high-tech PVC, have since become a selling point for schools, as more Chinese parents in the capital grow concerned about their children's health.
"It's certainly one factor I considered when I enrolled my son in Huijia last year," said Ms Yang Wei, 38. "We breathed clean air growing up, but Beijing children are not so lucky. They have been breathing bad air their whole lives."
Air domes were pioneered in the United States in the 1970s. Chinese companies acquired the technology and started to build their own domes about 10 years ago.
There are an estimated 200 domes in China. As is the case in the US, most are used as sports complexes because they are fairly easy to set up and temperatures can be controlled, which allows users to exercise whatever the season.
Still, only in the past few years have anti-pollution features been incorporated into their design, said Mr Gordon Gao, the general manager of the Beijing subsidiary of Broadwell, a major local dome maker.
Even though his company built air domes for the Chaoyang Sports Centre in 2010, it added air filtration functions only in 2013, after air quality worsened in the city. Broadwell also built the first air dome for a Beijing school in 2012.
"It's a uniquely China endeavour, using domes to counter smog," Mr Gao told The Straits Times.
At least five schools in Beijing have domes now, with manufacturers saying that interest spiked after the capital suffered its worst spell of smog in recent memory last month.
About 10 other schools in Beijing have recently made inquiries with Broadwell.
"With more schools getting domes, others feel it's becoming a necessity. Before enrolment, parents are already asking if the school has a dome," said Mr Gao.
One limiting factor, however, is the cost. A 3,000 sq m dome, which can fit half a dozen basketball courts, costs at least three million yuan (S$660,000), which is beyond the budget of most schools. Even if they can afford one, they might not have the space for it.
Still, dome or no dome, Chinese parents are increasingly taking charge when it comes to fighting smog in schools. More parents are digging into their own pockets to ensure clean air for their children at school, according to a China Daily report last month.
Mr He Zhenghuan, 42, organised one such effort for his 10-year-old daughter's primary school classroom more than a year ago.
Working together with parents from about a dozen other classes, he managed to get a bulk discount from an air purifier vendor. Each parent forked out 50 yuan.
"This is really the least we can do for our children," Mr He told The Straits Times. "Not everyone can afford domes."