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People cross an intersection on a hazy day in Beijing on July 20, 2017. Chinese cities had fewer 'good air' days in the first half of 2017 compared to the same period last year despite government efforts to curb incessant smog, according to official data. / AFP PHOTO / GREG BAKER (Photo credit should read GREG BAKER/AFP/Getty Images)

People cross an intersection on a hazy day in Beijing on July 20, 2017.
Chinese cities had fewer 'good air' days in the first half of 2017 compared to the same period last year despite government efforts to curb incessant smog, according to official data. / AFP PHOTO / GREG BAKER        (Photo credit should read GREG BAKER/AFP/Getty Images)