No quick fix to Beijing's pollution
BEIJING -- For all the fuss about the measures that Beijing is taking to clear its smog, the reality is that the blueness of the skies during the 2008 Olympic Games will have very little to do with Beijing's Potemkin village-style pollution control efforts, because the air pollution in Beijing comes predominantly from south of the city, riding winds and making the journey to the capital from up to hundreds of miles away.
Tiny pollution particles in the air, known as particulate matter, are what cause smog. Earlier this week,
If the relative humidity were near 100 percent, Rahn says, perhaps condensed water would be contributing to the haze, but the current relative humidity in Beijing is 70 percent, and yet visibility across the street is impaired. The fault, however, does not lie primarily with Beijing.
On days when the Beijing haze is at its thickest -- the smog on Thursday was the heaviest since late July -- around three-quarters of the particulate matter pollution is blowing in from provinces that ring Beijing to the south -- where coal power plants, including those that drive Beijing, are sprouting like weeds. Even if every car disappeared from the streets of Beijing tomorrow, there would be little impact on the clearness of the sky.
Take as an experiment the traffic modifications that Beijing introduced on July 20. That's when half of the city's cars, based on license plate numbers, were removed from the streets each day in an attempt to clear the air before opening ceremonies. Rahn has been graphing daily
What immediately jumps out -- or, actually, doesn't jump out at all -- is the absence of any effect from the July 20 traffic restrictions. The traffic modifications did nothing to dent the smog. In fact, the pea soup skies began to thicken in the days after the traffic ban, and pollution monitors as far away as the Great Wall, 70 miles outside of the city, where cars are hardly present, continued to record particulate pollution levels only slightly lower than those in the city. It was nearly two weeks after the traffic ban that the blue fully emerged.
But, even then, it had nothing to do with ban, nor will it hold for the entirety of the Games. Most likely, there will be blue days and brown days during the Games, because the smog is controlled not by Chinese motorists, but by regional weather patterns that, in the summer, run in roughly two-week cycles. For the better part of two weeks, pollution from the south blows in to Beijing, and then a cold front from Mongolia crashes in and blows it all away, and the cycle begins anew.
Rahn realized this on his first visit to Tsinghua University in November 2005. No sooner did he get to campus than a student plopped in front of him five years worth of data on air pollution, recorded every 30 minutes. "They said, 'Here, we don't know what to do with this,'" Rahn recalls. "It turned out to be an exceedingly clear set of data. I saw the basic story within minutes." For nine months of the year, the particulate pollution in and around Beijing follows a nearly weekly pattern, and in the summer, that pattern extends to two weeks:
1. On the first day, a cold front sweeps in from Mongolia, similar to the way cold fronts from Canada visit the Northeast United States.
2. The cold front tends to bring blustery winds, washing away the smog and delivering clearer air from the north. Again, this is similar to the winds from Canada that shove pollution out of New York City.
3. After a day or two, the incoming winds begin to shift counterclockwise, to the west, and then to the southwest, with the haze from industrial zones in tow.
4. As the wind shifts entirely to the south, the haze builds until another cold front form the north crashes in and wipes it away. The smog clears, and the cycle starts anew. In the summer, the cycle lengthens to two weeks, as opposed to every week, because the decreased temperature difference between the equator and poles slows down atmospheric circulation. (The
After a couple of terribly hazy days in late July, the sky cleared, and Beijing officials rejoiced at the prospect of an azure backdrop for the Games. But, barring more extreme weather patterns, like typhoons coming from the south of China that could deflect pollution around Beijing (one hit in late July), the atmospheric circulation in China will not pause for the XXIX Olympiad. "I want the Chinese people to have a high quality Olympics," Rahn says, "but you have to be realistic. Chances are [the air] won't be as good as they want."
The Chinese have their pollution fighting hearts in the right place, and they had reason to be hopeful that the traffic ban would bring blue skies. It appeared to do so in November 2006, during the two-day Beijing Summit of the Forum on China-Africa Cooperation. During the summit, large numbers of cars were taken off the road, and the skies were blissfully blue. But it happened to coincide with stronger than usual winds from the northwest.
When Rahn and Tsinghua University researchers measured particulate pollution last summer during a four day period in which 40 percent of cars where taken off the roads, "nothing happened," he says. "There was probably a small change, but it was undetectable."
Beside the pollution sweeping up from the south, Beijing faces one other indomitable foe in the smog wars: rain, or, really, lack thereof. Water in the atmosphere gloms on to pollution particles and drags them to the ground when it rains, clearing the skies. Beijing, located in a relatively arid region of northern China, gets just over half the annual rainfall of New York City. "It's like if you moved New York to the American West and expected to get clean air," Rahn says. Chinese officials have tried the dubious method of cloud-seeding, spraying particles into clouds to provide nuclei for rain drops, to increase the amount of pollution clearing rain, but cloud-seeding has never proven effective. Plus, the air at cloud level is moving, so even if rain clears one segment of air, it won't last. If the air at cloud level is moving at a reasonable 20 miles per hour, to clear the sky over an Olympic event for one hour would require clearing 20 square miles of sky, a completely unprecedented and probably outlandish feat.
Not that the traffic controls are totally worthless in reducing haze. Within the regional atmospheric circulation that causes the smog cycles, there are local cycles, with rush hours pushing pollution up somewhat, and wok-cooking bolstering particulate pollution at night. Beijing has done all it can with cars, and a wok ban would seem farfetched.
Still, by taking cars off the streets, and shuttering factories -- one large steel factory was even relocated to an island downwind -- and halting construction, Beijing officials have made an Olympian effort on the local level. Alas, if only the problem were local. According to multiple American scientists who work with Chinese researchers, Chinese officials have, in the last few months, begun to recognize that the smog is a regional problem, worsened by the new coal power plants that go online at least weekly in China. For the last few months, the scientists say, Chinese officials have started traveling to the provinces south of Beijing to remind local leaders that they have a duty to help ensure a pristine Olympics, and that they should consider enacting measures to reduce particulate pollution. But these southern provinces power Beijing, and the cost of shutting them down would be astronomical. Ultimately, Chinese officials are left to "pray to the Mongolian weather gods to send cold fronts," as Rahn puts it.
On the bright side, while particulate pollution has been shown to have an impact on exercise capacity, carbon monoxide, which crowds out oxygen in the blood, should probably be of more concern to athletes at the Games than smog, and the traffic ban may indeed impact carbon monoxide levels in some areas. Tune in to Part Two for more info on the impacts of particulate matter pollution and carbon monoxide on athletes.