An ongoing heat wave has British officials sounding the alarm over London's bad air quality.
On the eve of the 2012 Olympic Games, London is being gripped by a massive heat wave that has health officials concerned about athletes and visitors alike. According to top air-quality watchdogs at King's College London, high temperatures are making any ambient pollution even worse for people's health. The situation's so bad, the city has issued an official warning urging people to caution -- something it hasn't been legally bound to do since the last major heatwave, six years ago.
Could air pollution wind up affecting Olympians in competition? That was a big question for athletes in the last Summer Games, when Beijing was covered in gray smog right up until the opening ceremony.
The good news is, London is a major improvement over Beijing for the soot and other particulate matter floating in the air. Measurements show that Beijing had more than three times the amount of large airborne particles in the run-up to the Games than London did in all of 2011. Here's how London stacks up against other recent Olympic host cities:
These measurements were taken one month before the Games began at each site -- all except for London, whose number reflects the yearly average for 2011.