BLUE SKY BLUES #2: These two photos, taken two days apart on July 6th and 8th in 2008, illustrate the unpredictable air quality in Beijing ahead of the Games. Left: a clear blue sky over Tiananmen Square in the evening. Right: A smoggy afternoon near the main Olympics venue, where visibility was so low that the iconic "Bird's Nest" stadium could barely be seen from the nearby bridge where the photo was taken.