The Smog Free Tower, a 7-meter-tall large-scale air purifier designed by Dutch artist Daan Roosegaarde, has encountered skepticism from a number of experts since it began tests in Beijing.

Feng Jia, a member of the Chinese Society For Environmental Sciences, said that the tower is like hanging an air conditioner outside, and is therefore largely ineffective. It also produces some pollutants as it consumes energy, so it is just a kind of performance art, according to Feng.

Liu Guozheng, secretary general of the China Forum of Environmental Journalists, said that the tower is one of the forum's “smog reduction” activities. It serves as an educational event, which encourages citizens to do their part in reducing pollution.

Previous reports say the tower is capable of purifying 30,000 cubic meters of air per hour, and the smog particles it collects are compressed to make diamonds. Using ion technology and green energy, the tower captures at least 75 percent of PM2.5 and PM10 air pollution particles. In this way, it creates a large bubble of clean air around itself.

However, according to one expert, if the PM2.5 concentration is 200 per cubic meter, then the tower will absorb 4.5 grams of PM2.5 particles each hour, which barely equals the weight of a spoonful of salt.

Feng said the tower is quite effective in educating the public, but less so in reducing smog. He suggested that it be installed indoors instead.