Images of the Beijing skyline seemingly bathed in a soup of smog and haze have been a common sight on the world's TV screens in recent days and weeks.

Foreign journalists with hand-held air pollution detectors have been popping up on street corners checking levels of soot and dust. Everyone seems keen to prove that the city's air will be a decisive and debilitating factor for one of the world's most high-profile sporting events.

Without doubt Beijing is facing a huge challenge. There are real and understandable concerns for the health of competitors, especially those in endurance and long-distance events such as cycling and the marathon.