Three monks take selfies on a smoggy day in front of Bird's Nest Stadium, Feb.23, 2014. The Beijing Municipal Government upgraded its pollution alert from yellow to orange as choking smog continued to blanket the city. This was Beijing's first orange alert for heavy air pollution for the year 2014. The city has a four-tier alert system, using blue, yellow, orange and red to indicate the air pollution level in order of increasing severity. [Photo/Sina]