10/20/2014 02:36 pm ET Updated Oct 24, 2014

This Is What It's Like To Run A Marathon In Dangerous Smog Levels

Thousand of runners gathered in Beijing this weekend for the 34th edition of the city's international marathon. On their way from Tiananmen Square to the Bird's Nest stadium, athletes faced more than 26 miles of route, massive crowds and ... epic smog.

The South China Morning Post reported that as the nearly 30,000 participants lined up at the start of the route in Tiananmen Square on Sunday morning, the government had issued a blue alert for air pollution, which warns that the air quality is unsuitable for outdoor activities.

Beijing's official Air Quality Index topped 400 on the morning of the race, indicating a dangerously high concentration of PM2.5 particles per cubic meter. The tiny pollution particles, which are about 1/30th the average width of a human hair, are a health concern because when inhaled they can accumulate in the respiratory system. The World Health Organization recommends a daily average maximum level of exposure of just 25 micrograms.

Many runners appeared with face or gas masks at the start, according to CNN, and some pulled out off the race entirely. Instagram user RunningManMrj posted a video of the weather conditions, adding that he "had no choice to quit the game because of the terrible smog."

Many criticized the event's coordinators for failing to cancel the race, even though warnings about high pollution rates had emerged earlier last week. Organizers claimed they were unable to call off the mass event because many of the participants had traveled to Beijing from other cities or even from outside China.

Ethiopia's Girmay Birhanu Gebru was the first of the men to cross the finish line in 2:10:42.

Take a look at what it's like to run a marathon in Sunday's smog levels:


Sorry this is Beijing! #beijingmarathon #tiananmen #lifeisajoke #霾 #天安门 #北马

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Maratón en Beijing

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#beijingmarathon2014 #fogandhaze I have no choice but to quit the game all because of the terrible weather!!!

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#lofi #beijing #marathon #beijingmarathon #igersdaily

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Beijing Marathon