Almost half of all air purifiers made by companies based in Shanghai have been found to contain defects, a government quality inspection watchdog has said.

The General Administration of Quality Supervision, Inspection and Quarantine of China (AQSIQ) says that six out of the 14 batches of Shanghai-made air purifiers have failed tests for noise and purification efficiency, or are considered dangerous due to electricity leakage.

According to the AQSIQ, the problems are lengthy. Air purifiers made by Mitsubishi Heavy Industries Air-conditioners were found to have substandard efficiency for formaldehyde purification. Purifiers made by Baomi Information Science and Technology had noise problems, while Novowater air purifiers are described as having poorly protected electrical parts. ReFinAIR and Somputon air purifiers have problems with noise as well as “continuous disturbance voltage”, while products by Zhejiang Benyuan Appliance Co and sold by LongYea Environmental Technology  failed for particulate matter purification.

Last week, AQSIQ announced that nearly a quarter of the air purifiers sold on the Chinese market last year were substandard.

This past January, an air purifier made by Xiaomi was found to be have “serious problems” by the  Shanghai Quality Inspection and Supervision Bureau. The Xiaomi air filter was found to make excessive noise, and failed to process a sufficient amount of air in the room, commonly referred to in the industry as the “Clean Air Delivery Rate” (CADR).

The other three air purifiers found to be substandard by the Shanghai Quality Inspection and Supervision Bureau included Green Welcome (格瑞卫康) air purifier model GW9616 for “excessive noise”; the Envion air purifier model AP450 for “sub-standard CADR”; and the Three Papas (三 个爸爸) air purifier model AP-ANGLE for “standby power”.