Smog surrounds the Bird’s Nest, the Beijing National Stadium built for the 2008 Olympics. Photo: A. Aruninta. |
New research suggests that China’s
impressive feat of cutting Beijing’s
pollution up to 50% for the 2008 Summer Olympics had some help from Mother
Nature. Rain just at the beginning and wind during the Olympics likely
contributed about half of the effort needed to clean up the skies, scientists
found. The results also suggest emission controls need to be more widely
implemented than in 2008 if pollution levels are to be reduced permanently.
Reporting their findings in Atmospheric Chemistry and Physics, co-author atmospheric chemist
Xiaohong Liu at the Department of Energy’s Pacific Northwest National Laboratory
(PNNL) said, “In addition to the emission controls, the weather was very
important in reducing pollution. You can see the rain washing pollution out of
the sky and wind transporting it away from the area.”
Liu and colleague Chun Zhao at PNNL and at the Chinese
Academy of Sciences in Beijing took advantage of the emission controls China
put into play before and during the August Olympics to study the relative
contributions of both planning and nature. Chinese officials restricted
driving, temporarily halted pollution-producing manufacturing and power plants,
and even relocated heavy polluting industries in preparation for the games.
To find out if the controls worked as well as people
hoped, the researchers modeled the pollution and weather conditions in the area
before, during and after the Olympics. They compared the model’s results with
measured amounts of pollution, which matched well.
Adding up the sources of pollution and the sinks that
cleared it out, the team found that emission sources dropped up to a half in
the week just before and during the Olympics. And while some pollution got
washed out by rain or fell out of the sky, most of it got blown away by wind.
“They got very lucky. There were strong storms right
before the Olympics,” said Liu.
In addition to rain, wind also helped. Beijing is bordered on the south by urban
areas and on the north by mountains, so wind blowing north would carry more
pollution into the city. Examining the direction of the wind, the researchers
saw that it generally blew south in the time period covering the Olympic
period.
“The area we looked at is about 50 miles south. This
suggests that emission controls need to be on a regional scale rather than just
a local scale,” said Liu.
The importance of regional controls meshes well with previous
research on 2008 Olympics air quality that focused on nitrogen-based
pollutants.
Next, the researchers will be examining the effect of
pollution on other weather events and climate change in China.
Pollutants are very small particles, and some suspect they might be causing fog
to form rather than rain due to numerous pollution particles in China, Liu
said.
