The pollution that has shrouded vast areas in East China this month has seen sales of these appliances soar.

However, the market needs stricter supervision and higher national standards, experts said.

The pollution, especially concerns over high levels of PM2.5 — air particles smaller than 2.5 microns that are able to enter the lungs — has resulted in a surge of interest in air purifiers, said Song Guangsheng, director of the National Indoor Environment and Indoor Environmental Product Quality Supervision Center.

"Years ago, 80 percent of people who purchased purifiers did it to get rid of the paint smell in new homes," he said.

The national standard on indoor air cleaners, enacted in 2008, did not take into consideration the need for consumers to filter PM2.5 and increased use by consumers, he added.

Despite most air cleaners being effective in absorbing particulates, there are concerns over their effectiveness.

"Some producers boast their cleaners can handle 99.99 percent of air particles," Song said. "But these results are from tests covering an area of 3 or 4 square meters and within a time period of three hours."

According to a spot check on 20 air cleaner products by the Shanghai Bureau of Quality and Technical Supervision, only products by three producers indicated the space they can effectively function in, or reached the advertised standard.

Meanwhile, other products tested failed to indicate the occupied space in which the cleaner could function effectively.

Revision needed

A test of air cleaners by the Shanghai Consumer Council found some products failed to indicate clearly their performance data, with the Clean Air Delivery Rate — the cubic feet per minute of air that has had all the particles of a given size removed — of six products failing to reach their own target.

Eight of 22 products tested failed to mark clearly the effective space of the product.

"No matter whether it is a problem with the hardware or failure to state the performance data of the devices, they can mislead consumers," the organization said on Dec 6.

Song said a revision to the national standard, that requires air cleaners to mark clearly the occupied space in which the cleaner effectively functions, is needed.

"China doesn't have a comprehensive evaluation method for air purifiers, which makes the drafting of a renewed national standard difficult," he said.

Mo Jinhan, a researcher at Tsinghua University's Center for Building Environment Test, said the new national standard should also include their service life.

"Most cleaners work well and can filter particles. The only difference is the service life and maintenance costs," he said.

Various types of air cleaners designed to remove certain types of pollutants also make the drafting of a unified national standard difficult.

Song warns that air cleaners require proper maintenance and filters must be replaced on a regular basis.

"If the filters are not replaced, they will become a source of pollution because the air it distributes will be polluted," Song said.

Electronic air cleaners use a process called electrostatic attraction to trap charged particles but they must be used in a ventilated environment to discharge ozone generated in the process.

Lack of guidance

According to research conducted by the Building Services Research and Information Association, a market consultancy based in Britain, China will be one of the most vibrant markets for air cleaners in the next few years.

"Despite concerns over air quality, consumers have a low level of cognition of the industry and there is a lack of guidance on consumption," Yu Zhihui, deputy general manager of the agency, said at an industry forum in April.

He said the market is chaotic, as there is a lack of State-level certification and producers are exaggerating the effectiveness of products.

However, Yu said the market potential is not to be underestimated, as the usage rate in households was only 0.01 percent in 2011, much lower than in developed countries.

Despite the mixed reputation for air cleaners, Wu Jialu, a pregnant woman in Qinhuangdao, Hebei province, said she firmly believes that a filter is a necessity.

"It definitely helps make the air cleaner and the living environment better," she said, adding that her pregnancy has made her set higher standards for air quality in her home.

Wu said brand names remains key criteria for her selection.

"There are so many factors to consider and the producers should be required to mark clearly the technical standards of the products," she said.

xuwei@chinadaily.com.cn