Many people have been asking about the pollution. I've found this awesome site:
http://www.asiasociety.org/beijingair/?gclid=CJn19pDnjJUCFQnMXgodPSUtgA#room-with-a-view
Here we can see day by day the different pollution. Last year, when we had so many problems in the MTB test event (Sep 22), it says had a level of 99... Now, after all there efforts, the first few days of the games at levels of 95 & 94 !
It seems that the levels can change very rapidly and its more a matter of luck then anything else if we will be able to breath or not in our race!