Zhang Chao shows off the huge homemade air purifier he made after deciding the ones in shops were too dear.?[Photo/Xinhua]?

A?Shanghai IT professional made his own air purifier earlier this year.

Zhang Chao, who is in his 40s, said the air purifiers available to buy online and in shops are too expensive and not very efficient.

On taobao.com, some purifiers for household use cost more than 10,000 yuan (US$1,500), he told Shanghai Daily.

Zhang made his machine with parts he bought online — including an electric air cleaner made for industrial use — for about 1,000 yuan.

When he tested the machine for 13 minutes, the density of PM2.5 particles — as detected by the machine itself — fell from 166 micrograms per cubic meter to less than 10, he said.

He did not say if the methodology applied during the testing process complied with industry standards.

Zhang's machine is 1.2 meters high and 60 centimeters wide. Its scope is limited.

"The filter can handle tiny particles efficiently, but to filtrate pollutants like methanol and benzene, one would need to add a carbon filter," Zhang said.

He said he had spent more than 10,000 yuan over the past two years on air purifiers, but after they didn't work very well, he decided to make his own.

"After keeping a shop-bought purifier switched on for 24 hours, the PM2.5 level inside my apartment was only half what it was outside," he said.

He said he looked online for instructions on how to make an air purifier before making one.

Research by Shanghai Daily showed that there are numerous websites that provide such information.

After three months of using his homemade machine, Zhang calculated that it would cost him about 1,000 yuan a year to run.

The machine is not perfect, however, he said.

Without a heat exchange system, it can't control the temperature of the air it sucks into the room. It's not very good looking and it is noisy, he said.

"My family objected to the idea at first, as the machine looks raw and you need to knock a big hole in the wall to make it work, Zhang said.