In this photo by Ng Han Guan, a woman adjusts her mask during a heavily polluted day in Beijing. The city of 22.5 million people had a red alert for smog for a fourth day Tuesday. Schools were ordered closed, factory production was restricted and half the city's cars were forced off the roads each day. The pollution also obscured the skyline, affecting tourists visiting the Forbidden City. Winds were expected to improve conditions on Wednesday.