April
30, 2007
CHINESE
TRAFFIC
RESTRICTIONS YIELD QUICK AIR CLEANSING
Chinese
government restrictions on motorists during a three-day conference last
fall
cut Beijing’s
emissions of an important class of atmospheric pollutants by up to 40
percent,
recent satellite observations indicate. The November restrictions are
widely
viewed as a dress rehearsal for efforts by the city to slash smog and
airborne
contaminants when China
hosts the 2008 Summer Olympic Games.
The
restrictions on Beijing
drivers coincided with a
summit meeting on China-Africa cooperation from 4–6 Nov.
2006, during which an
estimated 800,000 of Beijing’s
2.82 million vehicles were taken off the road. Researchers now have
used
measurements taken from space to evaluate Beijing’s
air quality before, during and after the conference.
“Traffic
restrictions implemented during the Sino-African Summit were remarkably
successful in reducing emissions of NOx,”
report Yuxuan Wang of Harvard University
and her colleagues. NOx
is a class of nitrogen oxides formed during combustion and thought to
contribute to global warming. The research team assessed Beijing’s
emissions using data from the Dutch-Finnish
Ozone Monitoring Instrument aboard NASA’s Aura satellite,
which was launched in
2004.
“We
expected a drop in nitrogen emissions, but not to this extent, and
after only a
short period of time,” Wang adds. She conducted the study
with colleagues at
Harvard and at the Royal Netherlands Meteorological Institute in De Bilt,
Netherlands.
The scientists presented their findings 28 April in Geophysical
Research
Letters, a journal of the American Geophysical Union.
Past
satellite studies by other researchers have detected a
“weekend effect”—reduced
NOx emissions on weekends compared to
weekdays—over cities and
industrial areas in the Europe, Japan, and the U.S.
China
is the world’s second largest producer of greenhouse gases
behind the United States
and a major source of atmospheric NOx. Last
November’s driving
restrictions in Beijing
ranged from regulating access to specific roads to restricting use of
both
private and government vehicles.
The
size of the resulting NOx reduction surprised
Wang and her colleagues
in part because it departs from recent estimates. Those say that during
non-heating seasons, nearly 70 percent of NOx
emissions in the Beijing area
are from
vehicular emissions. Using this as a standard, the team calculated that
there
would need to be a 50 percent cut in vehicular use in Beijing
to account for the observed 40
percent drop in NOx. This stands in contrast to
the reported traffic
decrease of nearly 30 percent. “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,” Wang says.
Traffic
cutbacks expected this summer as practice for the Olympics, as well as
restrictions during the games themselves, will offer opportunities for
further
study of the processes determining the quality of air over Beijing,
she adds.
The
research was supported by the National Science Foundation.
##
Contact:
Peter
Weiss
American Geophysical Union
202-777-7507
pweiss@agu.org
This
text derived from:
http://www.agu.org/sci_soc/prrl/2007-10.html
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