Beijing's municipal government is considering the establishment of six air corridors to ease air pollution, which has returned just days after the weeklong Asia-Pacific Economic Cooperation meetings that gave rise to the term "APEC blue", according to the Beijing Municipal Institute of City Planning & Design.

Beijing's first blue alert on pollution since the APEC meetings was issued on Wednesday. Blue is the lowest of a four-level warning system. A new spell of smog is expected to begin on Saturday, covering major areas of northern China.

As the tight reins on production and vehicle exhaust were relaxed after the APEC meetings, pollutants accumulated again, with heavy pollution on windless days, said Zhang Dawei, director of the Beijing Municipal Environmental Monitoring Center.

Air corridors - wide tracts of land aligned in the direction of prevailing winds that help disperse pollutants and hot air in the city - are seen as a significant factor in easing pollution.

"Air corridors can help disperse and prevent the concentrations of small particulate matter, including PM2.5," said Liu Chunlan of the Beijing Research Institute of Environmental Protection. PM2.5 is particulate matter with a diameter of less than 2.5 microns that can penetrate the lungs and seriously harm health.

Her research team is engaged in identifying air corridors and conducting studies.

Peng Yingdeng, an environmental expert focused on city planning, said the design of air corridors is usually included in the planning stages of urban development.

In the city plan for Beijing in the 1990s, for example, areas between the Fourth and Fifth Ring roads were designed as air corridors or green belts to buffer the effect of the urban heat island and to preserve the city's ecology.

However, he said, such designs have mostly been ignored and have given way to economic interests in the construction of buildings. Re-establishing such air corridors could be challenging, Peng said.

Song Guojun of the School of Environment and Natural Resources at Renmin University of China said air corridors' effect on easing pollution is limited, especially considering that Beijing usually experiences smog when there's no wind.

"Air corridors are useless in that case," he said.

Starting Saturday, a new curtain of smog will cover major areas in northern China, including Beijing, Tianjin, Shijiazhuang and other major cities in Hebei province, because of the stable weather conditions that make it hard to disperse pollutants, the China National Environmental Monitoring Center said on Friday.

The coming spell, which may last for five days, is expected to increase the air pollution of these cities to heavy levels. In response, the governments need to issue orange alerts, the second-highest alert in the emergency system, the Ministry of Environmental Protection said.

The cities experienced good air quality during the APEC period, Nov 3-11, and residents called for blue skies to stay.

Chai Fahe, vice-president of the Chinese Research Academy of Environmental Sciences, said that the root solution to ease should be the reduction of emissions from major sources.

"The good air quality during the APEC period has proved that the reduction of air pollutants worked," Chai said.

(China Daily 11/22/2014 page3)