New York Times: The boys chronic cough and stuffy nose began last year at the age of 3. His symptoms worsened this winter, when smog across northern China surged to record levels. Now he needs his sinuses cleared every night with saltwater piped through a machines tubes. The boys mother, Zhang Zixuan, said she almost never lets him go outside, and when she does she usually makes him wear a face mask. The difference between Britain, where she once studied, and China is heaven and hell, she said. Levels of...