Experts are questioning whether a proposed canal from Beijing to Tianjin would reduce the capital's smog, as a new study suggested.

A bluebook by the Beijing Academy of Social Sciences said the 160 km canal, also capable of carrying ships, would start in southeast Beijing and end in the Binhai New Area of Tianjin.

This is not the first time the idea of building a canal has been brought up, but it has attracted attention because the bluebook said the canal may help reduce smog.

The microclimate effects the canal may have on Beijing can humidify the capital's air, reducing fine particles from such sources as industrial spray and dust, said the bluebook.

"But research results have shown that visibility decreases as the humidity grows, when the concentration of PM2.5 - particulate matter smaller than 2.5 microns that can penetrate the lungs - stays at the same level, which means moister air may not always be good," said Chai Fahe, vice-president of the Chinese Research Academy of Environmental Sciences.

He said it is laudable that experts from all areas are working on this issue, but every proposed method needs supporting data that have been scientifically demonstrated before jumping to a conclusion.

"Such a large body of water would certainly help regulate the microclimate of Beijing, but the water would have to be good quality and the project should not damage the existing ecosystem," Chai said.

The seawater directed into the canal would salinize soil along the canal. The water coming from the Bohai Sea, if poor quality, would not help improve Beijing's environment, Peng Yingdeng, a researcher from the Beijing Research Institute of Environmental Protection, told Beijing News.

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