Householders are being urged by consumers rights watchdogs to be on the alert for unqualified companies conducting bogus air quality tests in homes.

Residents complained to the Shanghai Commission of Consumers' Rights and Interests that some companies falsely claimed excessive levels of chemicals were being emitted by their furniture and tried to sell them air cleaning units.

One consumer, surnamed Li, said he was concerned that new furniture he had bought emitted a strong smell so hired an air-quality testing company he found on the Internet.

The company's report said that in Li's apartment formaldehyde levels were eight times higher than standard, and benzene 10 times higher.

Li was sold a nanometer air cleaner valued at 1,280 yuan (US$200) to remove the supposed hidden dangers identified by the company.

However, afterwards Li became suspicious and reported the firm to the commission.

A certificated air quality company conducted a second test and found no problems with air quality in Li's home.

The commission discovered the initial company had no air test license and its report was false.

The Shanghai Bureau of Quality and Technical Supervision has a recommended list of air quality test companies on its website www.shzj.gov.cn. Only a Chinese version is available.

Under China's laws, air quality testing companies are not allowed to produce or promote any air-cleaning products.

Test fees are usually between 600 yuan (US$93.7) to 800 yuan for each location, said bureau officials.