What can be hard to get across is exactly how much the smog changes the day-to-day life in the city. This photo, taken by Reddit user BananasUnited, shows the difference between a "clear" day, with a AQI of less than 500, 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.