Thousands battle smog in this year’s Beijing marathon

Runners wearing masks to protect themselves from pollutants jog past Chang’an Avenue near Tiananmen Square shrouded in haze while taking part in the 2014 Beijing International Marathon on Oct. 19.  (Andy Wong / Associated Press)

A runner takes photos as others jog past Tiananmen Gate shrouded in haze at the start of 2014 Beijing International Marathon.  (Andy Wong / Associated Press)

A professional runner has breathing difficulties during the Beijing Marathon. The smog forced some runners to quit the marathon.   (Chi Ben / EPA)

Runners, some wearing masks to protect themselves from pollutants, jog at Tiananmen Square shrouded in haze at the start of 2014 Beijing International Marathon.   (Andy Wong / Associated Press)

Runners jog past Chang’an Avenue near Tiananmen Square on Oct. 19.   (Andy Wong / Associated Press)

A runner, wearing a mask, jogs past Tiananmen Gate shrouded in haze.   (Andy Wong / Associated Press)

Runners compete in the Beijing marathon Oct. 19. Due to serious smog affecting the city, some runners were forced to quit the race.   (Chi Ben / EPA)