People in China's smog-hit northern cities are buying an unprecedented number of air-pollution-blocking masks and a British-made product is becoming a hit among well-informed buyers.

A cyclist wears a Respro face mask. [China Daily]

A massive number of face masks are available in the nation, including basic surgical masks, industrial face masks and reusable masks. However, critics point out that not all of them are effective in blocking out harmful particles.

Respro, a British-made brand, is among companies that are making a name for themselves in China because of their filter quality, functionality, style and originality.

The Respro mask was first sold in China about 10 years ago, primarily targeting expatriates living in the country. However, the company's sales rocketed in 2013 when the air quality index went well above 500 PM2.5 in some parts of the country.

Respro recorded a 500 percent rise in revenue that year and has since enjoyed a steady growth in sales of around 10 percent a year.

Lukas Thibaut, a Brit who has been living in Beijing for more than four years, said he started using Respro masks because they performed well in tests.

"I wanted a face mask that would be suitable for doing outdoor sports, so I ordered the ResproSportsta, which has extra-large valves to improve exhalation," he said.

Occasionally, Thibaut also uses the white, industrial face masks, which can be easily found in most convenience stores and are much cheaper, but he finds them uncomfortable to wear.

"They also don't look as cool as my ResproSportsta," he said.

Henry Cole, chief executive of Respro, said the material in most Respro masks was first produced by the UK defense establishment in the 1980s and was used to protect troops under the threat of nuclear and biological warfare.

Gary Fuller, senior lecturer in air quality measurement at King's College London, told China Daily: "Tests conducted in Beijing in 2009 found that the high-quality masks that are used to protect people working in factories can also help to reduce exposure to ambient air pollution."

Fan Chung, professor of respiratory medicine in Imperial College London, believes that the most effective masks available to reduce particle exposure are those that are labeled N95. They are able to filter 95 percent of airborne particles of greater than 0.3 micron, including the PM2.5 particles prevalent in the smog in China that are small enough to penetrate the lungs.

He said: "More expensive mask will have an exhaust valve to improve comfort while wearing the masks. Inexpensive cloth masks can be used but these are much less efficient in getting rid of small particles."

Chung said the long-term solution to the problem of environmental pollution is to reduce and suppress the sources of pollution, but this will take time to achieve, even with the best efforts available at all levels.