Visitors to Beijing's Tiananmen Square battle heavy smog on Jan. 31, 2013 (left), and breathe easy the next day, Feb. 1, 2013.
On the left, commuters on Beijing's second ring road experience heavy smog on Jan. 30, 2013. On the right, the same road on Feb. 1, 2013.
The Forbidden City in Beijing from the historic Jingshan Park (left) on Jan. 30, 2013, and during clear weather (right) the very next day.
Guotai Chambers (left) on Jan. 31, 2013, and the same shot the next day (right).
A security guard stands in Jingshan park in Beijing during heavy pollution (left) on Jan. 30, 2013. The park is clear on Feb. 1, 2013 (right).
This combination of photos shows a section of the Beijing skyline (left) during heavily polluted weather on January 30, 2013, and during clear weather the next day (right).