The Consumer Council on Monday called on manufacturers of air purifiers to clearly indicate how much clean air their products can deliver per minute.

The watchdog said clearly stating the clean air delivery rate would help buyers make better choices.

The council tested 10 air purifiers, and found big differences in their performance.

The best performing model was 12.3 times better than the worst at removing formaldehyde, while variations in their effectiveness in removing smoke ranged up to 2.7 times.

Speaking at a press briefing, the council’s chief executive, Gilly Wong, said the clean air delivery rate could act as a convenient metric for consumers to compare different air purifier models.

“Because the standards of filtration is quite different among different countries, no matter it is dust or pollens or cigarette smoke, it's quite diverse,” she explained.

“It is easier for consumers to compare based on the CADR - the clean air delivery rate.”

The Department of Health reminded consumers to clean their purifiers regularly to minimise the risk of diseases, while the Hong Kong Medical Association reminded people to maintain air circulation by keeping windows open to ensure indoor air quality.