1 / 6   The serious air pollution in China has greatly boosted sales at mask factories, which enjoy huge profits. /CFP Photo

2 / 6   Factory workers race against the clock to meet the surging demand from the market. /CFP Photo

3 / 6   Since last November, workers at mask assembly lines in a factory in Xiamen, east China’s Fujian Province have lifted their workload, working from 8 a.m. to 11 p.m. every day, yet they still cannot catch up with market demand. /CFP Photo

4 / 6   In December last year, orders increased by 20 times the average level. Currently there are nearly 1,000 anti-pollution mask producers across China, according to Xinhua News Agency. The number in 2013 was just 500. /CFP Photo

5 / 6   However, the quality of domestically-manufactured anti-pollution masks is worrying. A recent report by the quality inspection bureau of Jiangsu Province showed that 99 out of 160 batches of masks didn’t meet China’s quality standards. /CFP Photo

6 / 6   Factory workers race against the clock to meet the surging demand from the market. /CFP Photo