Beijing's Migrant Smog Problem

Where Does the Capital's Air Come From?

Among environmental scientists and cab drivers alike, the cause of Beijing’s pollution—and thus how to stop it—is an old topic of debate. Now, thanks to a municipal research program to clear the air for the “Green Olympics,” it’s a $3.2 million question. If the task were as easy as shutting down local factories, phasing out coal-fired heating, cleaning up power plants, and restricting traffic during the Games – plans already being carried out by officials – Beijing would be on course. But as researchers have realized in recent years, much of Beijing’s dirty air is drifting in from outside. But figuring out from where, and what to do about it, is looking much more complicated than anyone expected.

“The general implication is that it’s not going to be so easy to clean up Beijing for the Olympics,” says Kenneth Rahn, an environmental engineer and visiting scholar at Tsinghua who works with the university’s Air Pollution and Control Institute. While his students study everything from ozone to nasty sulfur dioxide, Rahn’s passion is aerosols, or the microscopic particles that create haze and may contribute to health problems when lodged in the lungs. These days, Rahn is seeing a lot of the stuff coming from outside Beijing. “If you focus on Beijing alone, you’re only controlling half the problem.”

The usual suspects – that is, metal smelters in Inner Mongolia, Mongolia, and Western Siberia – appear to be the source of much of Beijing’s external pollution. But as Rahn and his team are learning from their measurements, much of Beijing’s imported pollution is also coming from coal-fired factories and cars to the south of Beijing, from areas as far away as Shandong province, Henan province and Shanghai. The implication is that these areas too may need to clean up ahead of the Olympics. “This is something really new,” Rahn says.

During a typical pollution cycle, Beijing first feels its smog-carrying breeze from the northwest. Then, winds from the south begin to pick up, traveling easily across the flat coastal region that Rahn affectionately refers to as The Bathtub, for the way dirty air here easily “sloshes” around. When it arrives in Beijing, the migrant smog mingles with local particulate matter—until a cold front or rain washes it away in the direction of Korea, Japan or even the U.S., leaving behind a few days of blue Beijing skies.

But how many days of blue skies will Beijing get during the Games—and will the city meet Olympic air standards as promised? According to Rahn, while Beijing’s pollution cycles become weaker and less frequent in summer, they begin to reappear with moderate strength in August, just when the athletes roll into town. “That means that the degree of air pollution during the Summer Olympics is purely a matter of chance,” he says. Blue skies could happen, he says, but “if you forced me to take a guess, I would say [Beijing] won’t meet the standard.”

For the future, Rahn says China needs stricter emissions controls on cars and policies like the U.S.’s landmark 1970 Clean Air Act, which enforced pollution standards for all new factories and power plants. “It’s not about the Olympics but the next fifty years.” For the time being though, his advice to Beijing’s Olympic planners is simpler: “Best to pray to the Mongolian Weather Gods.”