pollution increases after the olympics

We are now one month past the end of the temporary air pollution reduction policies put in place for the Olympics and Paralympics. As expected, pollution levels have gone up. But how much? Using PM10 concentrations as an indicator, I estimate that the air quality in Beijing for the past month has been around 24% worse than it was during the two-month Olympic period. The pollution has actually been worse this past month than it was during the same period in 2007, though still significantly better than the same period in 2006:

It should be noted, though, that the averages over this past month are slightly skewed by the extreme pollution of this past Saturday (October 18th), when the API shot up to 174 (PM10 concentration 298 ug/m^3). This was the first day with an API above 150 since June.

Saturday's brutal - but short-lived - high pollution event raised a question in my mind that I'm not sure the answer to. From a health perspective, should we worry more about these short-lived extreme pollution spikes or long-term elevated baseline levels? For PM10 specifically, the WHO gives both daily and annual targets (50 and 20 ug/m^3, respectively). Granted, Beijing's air quality regularly exceeds both, but which is likely to cause more damage?

Lastly, it should be noted about the above table that I have done a direct conversion from API to PM10 concentration using the formulas at the bottom of this post, although this is an imperfect system because China does not list the primary pollutant for APIs below 50. Given the fact that PM10 is almost always the primary pollutant when the API is above 50, I think it's a reasonable approximation.