When Beijing's air pollution hit record levels in January last year, personal secretary Li Mengwan, 32, spent 6,600 yuan (S$1,400) to buy two air purifiers for her home.
When air pollution levels again spiked this January, she bought a third one, costing 1,600 yuan.
Some may find three air purifiers too many, but Ms Li and her husband are not taking any chances, as they have a five-year-old daughter, and her elderly parents also live with them.
"One can never have enough air purifiers in Beijing, especially when the air quality is bad," she told The Straits Times.
China's choking pollution may be posing health problems for ordinary people such as Ms Li.
On the flip side, however, it is helping to breathe new life into certain companies or spawn new business opportunities for others.
These include manufacturers of air purifiers, protective masks and "clean air inflatable domes", used in schools to allow students to exercise safely in a pseudo-outdoor environment.
The problem has also given rise to many air quality monitoring apps. The total user base expanded to 400 million this year, up from 100 million last year, analyst Liu Youyue of Zero Power Intelligence business consultancy told The Straits Times.
But the biggest beneficiaries of China's growing "clean air" economy are probably the makers of air purifiers, which are increasingly being snapped up by health-conscious and affluent Chinese consumers, say analysts.
Some 2.4 million units were reportedly sold last year, a big leap of 90.5 per cent from 2012.
China-based research institute AVC estimated that the air purifier market could grow to 75 billion yuan next year, up from 20 billion yuan this year and 12 billion yuan last year.
Business prospects are even brighter over the long term, as air purifiers are said to be used in only 1 per cent of Chinese households, compared with some 70 per cent in South Korea and 40 per cent in the United States and Europe.
The immense growth potential has lured even Internet companies into the fledgling market. The latest entrant is smartphone maker Xiaomi, which began selling its 899-yuan phone-controlled Mi Air Purifier just last week, joining other Internet firms in the market.
Science-themed social networking site Guokr is selling a 1,984- yuan egg-shaped product dubbed Xiaodan, while phone app maker Cheetah Mobile unveiled its 998- yuan Baomi product in October.
One key reason for the brisk sales was a move by China in 2012 to monitor and publish its own Air Quality Index readings around the country, say manufacturers and analysts.
Since then, more than 80 monitoring systems have been installed in major Chinese cities, raising public awareness about air quality and how to protect oneself.
Thanks to the move, Shenzhen-based Vortek Group, which saw flat sales when it started selling air purifiers in China in 2008, has seen a big boost in business since 2012.
Mr Dai Ming, manager of the company's air purifier department, said it sold some 40,000 units this year, more than four times the 9,000 sold in 2012.
"The biggest increase in demand for our products comes from Beijing and northern Hebei province," he told The Straits Times, citing two places where air pollution is known to be the most severe.
The rapid expansion, however, has led to a chaotic market, with no clear standards on the products and their performance. A recent spot check on 20 air purifiers by the Shanghai authorities found only three functioning effectively, according to the specifications.
A draft national standard was introduced late last month in an attempt to regulate the market, and is expected to be passed in the next few months.
This article was first published on December 22, 2014. Get a copy of The Straits Times or go to straitstimes.com for more stories.