Act earlier to ease smog’s grip on Beijing, scientists urge authorities
Curbs on factories and cars need to be imposed earlier to minimise effects of pollution, research team suggests
Ordering polluting factories to shut down well before smog looms would go a long way to easing the effects of choking air contamination shrouding northern China, a team of mainland scientists has found.
Beijing and surrounding regions have been engulfed in repeated waves of pollution in recent weeks, prompting the authorities to issue smog alerts, order manufacturers to halt production and impose traffic restrictions on private cars. But it has all been to little effect.
That was because the action came too late, the researchers, led by professor Wang Yuesi from the Institute of Atmospheric Physics at the Chinese Academy of Sciences, said in a statement on Friday.
Much of the smog comes from heavy industry south of Beijing.
It is usually dispersed by winds from the north but when those winds abate, can be carried north to the capital by warm air from the loess plateau.
When it reaches Beijing, it plunges rapidly to ground level and mixes with local vapour and vehicle exhaust, causing “explosive growth of secondary particulate matters”, according to the researchers.
By the time the government imposes the curbs on vehicles and factories, pollutants have already built up in the atmosphere about 500 metres to 1km above the heavy industry sites south of Beijing, according to radar echoes examined by Wang and colleagues.
Therefore ordering factory shutdowns and car curbs after the smog was on the horizon would have little effect.
The researchers suggested that heavy industry be shut down when weather forecasts indicated the winds would carry the pollution north. If heavy emitters in source areas could cease production beforehand, severe pollution could be prevented.
“Pre-warning should be implemented two or three days ahead of the heavy haze coming, and the regional stationary emissions especially the elevated sources should be controlled and reduced in advance,” Wang and his colleagues said.
The method, coupled with local emission control, would efficiently lower the peak values of contaminants, they said.
The researchers said the suggestion had been submitted to the Ministry of Environmental Protection.
Kang Ling, senior engineer with Peking University’s College of Environmental Sciences and Engineering, said the team’s suggestion made sense, but it would not be as effective in clearing the air as the northerly winds.
“Human intervention has so far had little effect. To drive smog away, we still rely almost exclusively on wind,” Kang said.
Dr Hu Yongtao, senior research scientist at the Georgia Institute of Technology’s School of Civil and Environmental Engineering, said introducing the curbs two or three days earlier could reduce potential peaks in pollution.
But the study had limitations. “It only explains one certain type of pollution episode in Beijing, and that there are also gaps in their hypothesis and theory which need further research by other means,” Hu said.
For example, the mechanism that sent pollutants in higher altitudes to lower levels was not known.
“It is tricky to know what exact actions should be taken during certain types of episodes and how to quantitatively implement them,” he said.
The accuracy of smog forecasts was also a factor. Forecasts were reliable up to 120 hours but not beyond that, and within that period there could be mistakes, Hu said.
“Even with much longer lead time, unless you ‘empty’ the entire city and the region as was the case during the ‘Apec blue’, [the pollution would not go away],” he said.
“Ultimately air quality improvements must come from solid long-term pollution control.”