Overseas forerunners
Alan Robins, a professor of Environmental Fluid Mechanics from the University of Surrey in the UK, said many cities around the world are considering the benefits of opening-up dense city centers to allow better wind penetration.
"Better ventilation will reduce pollutant concentrations from local sources but make little or no change to pollutants transported from afar, so the answers depend on the cause and sources of pollution," Robins told the Global Times.
To seek greater use of natural ventilation and smarter design, he said a major new research project called MAGIC (Managing Air for Green Inner Cities) has just begun in England.
Ng cited Stuttgart as one of the best example of using ventilation corridors.
Lying in a valley, the industrial city's heat and pollution became dire in the 1970s. Gradually, the city begun to create large interconnected green areas and disallow new construction in ventilation corridors, policies which have been largely successful, according to the WWF.
"Officials need to change their conception of development and balance the land's economic and environmental benefits," Ng suggested. "As the problem of food and clothing has been solved, people have started to seek a more healthy life, and they demand clean air."
In an interview with Phoenix TV last week, Xie Zhenhua, China's Special Representative on Climate Change affairs, also emphasized the necessity of urban ecological corridors.
"If it has no such corridors, the city must have design defects. The city of Beijing is characterized by urban sprawl, which is unscientific," said Xie.
In China, the urban land price keeps rising and income from land transfers and commercial development has become a major source of finance for local governments. Policymakers seldom prioritize green spaces.
Yu said the Wuhan climate map, which demarcates no-build zones in wetlands and ventilation passages, has been strongly resisted by local officials.
"They are eager to develop those zones," Yu said. "The only way to stop them is legislation, which city planning officials and experts are promoting."
In Stuttgart, supported by legislation, over 60 percent of the land is covered in green and the city has prevented over 60 hectares from being built on in recent years, said the WWF.
To improve wind conditions, the Hong Kong government officially adopted its Air Ventilation Assessment System in 2006 following the severe acute respiratory syndrome (SARS) outbreak which killed nearly 300 people in the city.
Ng said the system requires all major publicly funded development projects to undertake an assessment and make the results public, so as to ensure buildings do not hinder the city's ventilation.
Wind slowing down?
According to the Beijing planning commission, the five larger ventilation corridors in Beijing will mainly consist of parks, lakes, roads and green space, and nearly all run north to south as northerly winds prevail in the city.
Quoting unnamed designers for Beijing's ventilation network, Xinhua reported that massive demolition won't be necessary to create these corridors. But there are quite a few high-density neighborhoods blocking the passages, such as the Shilihe area in the southeast corner at the Third Ring Road, where demolition will be carried out slowly.
Some worry that the corridors might increase pollution in suburbs. The designers denied this, telling Xinhua that the pollutants will be diluted gradually or blown into the upper atmosphere.
But Yu said he believes that the planned design for five separate corridors in Beijing is not the optimal system.
Professor Ng agreed. "A complete ventilation system should be interconnected. Like a lung for the city, the system can only be effective when the main corridors, branches and smaller ones are all formed and work together," he noted.
However, Yang Xuexiang, one of the few experts who believe the wind slowing down contributes to the increasing presence of smog, said the ventilation corridors are useless when there's little wind.
"The wind in North China has slowed down, partly due to excessive exploitation of wind power and building of windbreakers, which could affect the spread of atmospheric pollutants," Yang, a retired professor from the College of Geo-exploration Science and Technology, Jilin University, told the Global Times.
A study published by the journal Nature Geoscience in 2010 found that the average annual surface wind speed in countries in mid-northern latitudes - including the US, China and Russia - had dropped by as much as 15 percent, from about 17 kilometers an hour to about 14 kilometers an hour, and that trees may be to blame.
Currently, to prevent seasonal sandstorms from coating Beijing in material from the Gobi desert, belts of trees have been planted around the city.
Yang argues that these trees should be replaced with shorter shrubs and other plants to allow the wind to blow faster.
