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, Arne Ljungqvist, chairman of the IOC medical commission, scolded the media for harping on the smog, and said that the Beijing haze is fog, not pollution, an suggestion that Kenneth Rahn, a professor emeritus at the University of Rhode Island who has been studying the pollution in conjunction with Beijing's Tsinghua University, says has "not much more than" a grain of truth.
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 the particulate matter pollution using data from the Beijing Environmental Protection Bureau.
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 pollution data for August 6 looked slightly better than August 5. But Rahn suspects that the current two-week cycle has a few days to go, and that in the absence of rain, the day of opening ceremonies could the worst since the media poured in to Beijing last week).