Since winter, when Beijing was shrouded in smog and pollution levels went off the charts, many expatriate residents have been asking themselves one question: Should we stay or should we go? The latter ...

and a smoggy day, with an AQI of more than 500. AQI stands for Air Quality Index, which technically only goes to 500. On January 29th, however, Beijing's AQI reached 517.

Photographs of Beijing on a smoggy day (June 19, 2009) and a blue-sky day (June 22, 2009), courtesy of China Air Daily. (Lin Yang and John Billingsley/Asia Society) China Air Daily, a project of Asia ...