Experts have called for a renewed national standard on air purifiers and for producers to clear the air on their effectiveness.

The pollution that has shrouded vast areas in East China since December 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 about 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 in which they can effectively function, or reached the advertised standard.

"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.

Meanwhile, 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 clearly indicate the effective space in which the product can function.

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.

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

Mo Jinhan, a researcher at Tsinghua University, said the new national standard should also include the product's service life.

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

Song warned that air cleaners require proper maintenance and that 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.

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