Last week, we reported on how China's herculean efforts to clean up Beijing's air ahead of the Olympics wouldn't work if the weather didn't cooperate.

Starting last Sunday, the air-cleaning regimen went into effect. Some trucks were banned from the road, traffic curbs were instituted, regional factories were shut down and in-city construction work stopped.

But yesterday, at least, the weather didn't cooperate.

Take a look at this picture snapped by our friends at the Chinese research firm, Pacific Sun Investment Management, at 3 o'clock Beijing time yesterday from the 20th floor of a building in the Central Business District.

Surely, air like this would send off air-quality alarm bells, right? Well, any day with enough particulate matter in the air to register over 100 on China's pollution index is considered bad. Over the last decade, Beijing has been measured to regularly reach 200, and sometimes even 500. The day this picture was taken rated a mere 113, or "slightly polluted," on the possibly rigged official rating. Yikes: what would a 300 look like?

If you're interested in following along as China conducts one of the largest atmospheric science experiments ever, check out the new Beijing air quality widget over at the Wall Street Journal's blog about China.

Image: Credit/Andy Tian, with an assist to Sage Brennan