China offers case study in atmospheric emissions

A traffic-cutting experiment, conducted last November in Beijing, has yielded impressive results.

The Chinese government's restrictions on Beijing motorists during a three-day conference succeeded in cutting the city's emissions of one important class of atmospheric gases by 40 per cent.
 
It was widely viewed as a dress rehearsal for efforts to slash smog and airborne pollutants during the 2008 Summer Olympic Games in Beijing.
 
That's the conclusion of Harvard University researchers Michael McElroy, Yuxuan Wang and K. Folkert Boersma, who used data from the Dutch-Finnish Ozone Monitoring Instrument (OMI) to assess the drop in emissions.
 
"I don't think a proper analysis has ever been made before of such a remarkable shift of environmental policy in such a short period of time," said McElroy, a Professor of Environmental Studies in Harvard's Faculty of Arts and Sciences and School of Engineering and Applied Sciences.
 
China's restrictions on Beijing drivers coincided with the Summit of the Forum on China-Africa Cooperation, which took place between 4 - 6 November 2006 and during which an estimated 800,000 of Beijing's 2.82 million vehicles were taken off the road.
 
The OMI - aboard NASA's Aura satellite, launched in 2004 - documented a 40 per cent reduction in NOx, a class of nitrogen oxides formed during combustion, while the restrictions were in place.
 
These greenhouse gas emissions are thought to contribute, in part, to global warming.

Breaking down nitrous oxide

"Traffic restrictions implemented during the Sino-African Summit were remarkably successful in reducing emissions of NOx," said Wang, a postdoctoral fellow in Harvard's School of Engineering and Applied Sciences.
 
"We expected a drop in nitrogen emissions, but not to this extent, and after only a short period of time."
 
The measured reduction may also imply a more effective regulatory strategy than has been presented by the Chinese media.
 
Recent estimates say that during non-heating seasons, nearly 70 per cent of all NOx emissions in the Beijing area are from vehicular emissions.
 
Using this as a standard, the Harvard team calculated that there would need to be a 50 per cent reduction in vehicular use in Beijing to account for the observed 40 per cent reduction in NOx.
 
This stands in contrast to the 30 per cent reduction reported by China.
 
Wang is quick to downplay this inconsistency: "We're not sure what this means, and there will definitely need to be more detailed data on vehicle energy usage, like gasoline sales data, to develop a more precise value," she said.
 
Last November's driving restrictions ranged from regulating access to specific roads to restricting use of both private and government vehicles.
 
China, the world's second largest producer of greenhouse gases behind the United States and a major source of atmospheric NOx, is expected to duplicate these traffic restrictions during the 2008 Summer Olympic Games.
 
"I think the real value here is that these kinds of restrictions can really bring about significant change," commented McElroy.
 
"Coordinated observations on such occasions can provide precious opportunities to test and refine our understanding of atmospheric chemistry not only for Beijing but also for the large region of East Asia," he said.
 
The scientists detail their work this week in the journal Geophysical Research Letters.
 

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