Even by the city's standards, Beijing was very polluted on Sunday. The PM2.5 scale, which measures the number of micrograms of "particulate matter" per cubic meter, came up to a whopping 344. (To put that figure in perspective, the World Health Organization considers 25 micrograms to be healthy). ...
To say the least, these weren't ideal conditions for a marathon. But that race is precisely what took place on Sunday, as tens of thousands of runners braved the conditions to complete the 34th annual Beijing International Marathon.
Event organizers were aware that the air wouldn't be good on Sunday, but determined it was too late to postpone the race, which had attracted participants from throughout China and around the world. To help runners clean detritus from their skin, organizers supplied over 140,000 sponges placed at stations throughout the course.
--Matt Schiavenza, The Atlantic, on taking air pollution to the next level