Mother nature helped cut Beijing's air pollution up to 50 percent during 2008 Olympics.
They found that rain just at the beginning and wind during the Olympics likely contributed about half of the effort needed to clean up the skies.
The results also suggested emission controls need to be more widely implemented than in 2008 if pollution levels are to be reduced permanently.
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 modelled 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.
The findings have been published in the journal Atmospheric Chemistry and Physics, December 12.