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Beijing Temporary Traffic Restrictions Cut NOx By 40%

The Chinese government’s restrictions on Beijing motorists during a three-day conference last November succeeded in cutting the city’s NOx emissions by 40%.

Harvard University researchers Michael B. McElroy, Yuxuan Wang, and K. Folkert Boersma used data from the Dutch-Finnish Ozone Monitoring Instrument (OMI) to assess the drop in emissions. The scientists detail their work this week in the journal Geophysical Research Letters.

China’s restrictions on Beijing drivers coincided with the Summit of the Forum on China-Africa Cooperation from 4-6 November 2006, during which an estimated 800,000 of Beijing’s 2.82 million vehicles—about 28%—were taken off the road. The OMI—aboard NASA’s Aura satellite, launched in 2004—documented a 40% reduction in NOx while the restrictions were in place.

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.

—Michael McElroy

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% of all NOx emissions in the Beijing area are from vehicular emissions. Using this as a standard, McElroy, Wang, and Boersma calculated that there would need to be a 50% reduction in vehicular use in Beijing to account for the observed 40% reduction in NOx. This stands in contrast to the 30% reduction reported by China.

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.

—Yuxuan Wang

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.

—Michael McElroy

McElroy, Wang, and Boersma worked in collaboration with NASA and Henk J. Estes and J. Pepijn Veefkind of the Royal Dutch Meteorological Institute. Boersma worked on the OMI satellite instrument in the Netherlands before joining Professor Daniel Jacob’s atmospheric research group at Harvard. The research was supported by the National Science Foundation.


Rafael Seidl

For reference:

the PROC tracks European emissions standards. Euro 3 came in to effect for newly licensed vehicles on Jul 1, 2005 but only in Beijing. The step up to Euro 4 is due on Jan 1, 2008. Nevertheless, expect severe traffic restrictions for the sake of air quality during the Olympic Games.

Elsewhere, a delay of roughly 2 years was granted: Euro 3 by Jan 1, 2007 for diesel, and Jul 1, 2007 for gasoline. The step up to Euro 4 will follow in 2010.

In other words, China appears to be raising the bar as it feels it can given that it is still an emerging economy. Nevertheless, the combination of filthy legacy diesels (especially in commercial vehicles) and extremely traffic volume adds up to a lot of NOx in e.g. Beijing.

Compounding the problem are the large variations in fuel quality, which makes fine-tuning the injection logic that much harder. Sulfur content in diesel fuel is still as high as 2000ppm nationwide, with only some cities mandating 500ppm - i.e. harmful PM emissions are also sky-high.

China's leaders are acutely aware that general environmental degradation was one of the factors that led to the collapse of the Soviet empire. However, they are unwilling to rein in rapid economic growth and the associated traffic volume. The public's tolerance of continued Communist party rule appears to depend on it.

kit P

This might work for American cities. SUVs could only be driven if there was a snow emergency.


Or Mexico City, where each car is given a tag, on one of the five working week days this car cannot be driven on the road; the person must use transit, car pool or work from home on that day. Any day in the week would result in a (max) 20% drop in emmissions. Why wouldn't this work in North America? Service vehicles exempt of course.


It might work, but people probably would not stand for it any more than they would stand for Ross Perot's $.50 per gallon per year gas tax increase back in the 1992 election.

American's want their cake and eat it too. They are so used to science and technology giving them miracles that they just wait for the next breakthrough to solve all their problems.

Charlie Peters

Does ethanol fuel policy increase oil use and profit?

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