Runners training for a marathon often take special precautions to acclimatize to the weather, elevation, and obstacles they might encounter in their upcoming race. But runners at the recent Beijing marathon might have had to suck on a tailpipe to prepare for that city's conditions.

According to staff at the U.S. Embassy in Beijing, the air pollution during the race was hazardous. But marathon organizers went ahead with the event, claiming that it would be too difficult to cancel or reschedule. Thus, about 30,000 runners lined up at the start line for the Beijing International Marathon, some wearing face masks or even full-on gas masks to filter out the fine particulate matter in the gray smog that enveloped them.

The current air pollution standard is 25 micrograms of particulate matter per cubic meter. Beyond this level the air is considered harmful to breathe, according to the World Health Organization. A level of 300 micrograms of particulate matter is considered hazardous. The particulate matter level around Tiananmen Square reached 400 micrograms per cubic meter on the day of the marathon.

Race organizers handed out 140,000 sponges “to clean skin that has been exposed to smog," but a backlash has been growing over their decision to go on with the event. Check out these tweets:

Race organizers did note that some runners dropped out of the race citing breathing problems as the cause. But race winners, Ethiopians Girmay Birhanu Gebru for the men Fatuma Sado for the women, still managed to clock respectable times of 2:10:42 and 2:30:03, respectively. Both ran without masks.

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