Not so bad. That’s what Olympic Canadian cyclist Svein Tuft thought of the air quality when he raced on Saturday, Aug. 9 (Air Pollution Index: 78) for six and a half hours outside of Beijing. As The New York Times reported, Tuft made short shrift of the pollution fears:

The pollution concerns, he decided, “have been a massive hype.”

And Tuft isn’t alone in his pollution dismissal. Wimbledon champion and Spanish tennis player Rafael Nadal told the Associated Press, “The problem is the humidity, no? … The (truth), I didn’t feel nothing (from) the pollution. That didn’t affect … me. The problem is the humidity. I had to change the shirt every 10 minutes.”

Contrary to the highly-anticipated Olympic pollution angst (ahem … me), athletes have yet to throw up their hands in disgust because of Beijing’s air. With reason: Since competition began, the air has been rather good by Beijing’s standards. The highest API, 94, since the games opened was read on the the Aug. 8 opening ceremony. The next day, it plunged 20 points — even more in the Olympic venues outside of the city. The thunderstorm Sunday that forced the Beijing Organizing Committee (BOCOG) to reschedule tennis, archery, and rowing events also more than halved the API, which on Monday, Aug. 11, registered a 38. Sam Querrey, a U.S. tennis player, told the Associated Press:

I think the rain this last day and a half helped. But the first two days when we got here, I was struggling with the pollution, the heat, the humidity … You could really feel it in your lungs when you started to breathe heavily.

What gives? China Journal reports that the week of Aug. 15 to Aug. 21 averaged an API of 38, however when spectators and athletes first started to arrive in Beijing, an API in the 80s, 90s, or even low 100s was not uncommon. One Olympic spectator in Beijing told Grist that she first arrived she was astonished by the amount of pollution and never could have imagined it to be so bad. Sally Jenkins and Dan Steinberg, two writers from The Washington Post sports desk, went jogging in Beijing on the day of the opening ceremony and Jenkins said after that she felt “nasty,” and added that it felt like spending “all day at a NASCAR race.”

It turns out that it was probably a good thing that China did not (or could not?) make good on its boasts for weather-modified, “rain-free” Olympic games. As the games played on, the only force that substantially cut Beijing’s air pollution on a dime was the weather. Writing for Sports Illustrated, David Epstein described the two-week weather cycles that drive pollution into and out of Beijing during the summer:

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.

Kenneth Rahn of the Graduate School of Oceanography at the University of Rhode Island explained the weather patterns to Epstein:

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.

Rahn created a slideshow (requires Internet Explorer) to show the effects of the atmospheric weather patterns in Beijing (the 14th slide in particular shows the cyclical wind pattern Rahn described above). From his data analysis, Rahn commented in the slideshow:

Aug 19th (Tuesday): We now have enough data to better evaluate the plot of running averages. It seems to be divided into July vs. August, both of which have short-period and long-period cycles. At the beginning of August, the whole pattern dropped down by 20–30 API units. I first thought this was a downward trend during the first half of August, but it now appears to be more of a step function. It is more consistent with meteorological changes than with control efforts, which if they had kicked in rapidly, would have done so on July 20th rather than two weeks later. Thus I see this pattern as arising more from Mother Nature than from pollution controls.

In addition to Rahn’s data, the China Journal has a flash interactive (click “detailed view” in the “Beijing Air Quality” box) that presents three years’ worth of API data for Beijing. Scrolling through Beijing’s air readings, there is a phenomenon that the API falls in the summer and then starts to rise in late September. This is clear for the 2005 and 2006 summers. In 2007, it’s more noticeable just for the month of August, but all of these natural decreases took place well before any Olympic pollution controls were put in place.

This observation begs the question: Will these pollution measures have any lasting effect? Especially now that Beijing has vowed to “adopt strict new measures to ensure its notorious smog does not return,” would any action short of regional or national in scope make any effective difference?