ics, Chinese Academy of Sciences. The goals of the network were to monitor and provide warnings of the atmospheric quality in Beijing and its surrounding area during the Beijing 2008 Olympic Games. The results showed that the atmospheric complex pollution exhibited high concentrations of ozone and fine particles and oxidation in summer, with a ubiquitous regional source. The regional mean concentrations of SO 2 , PM 2.5 , NO 2 , and O 3_8h max (the maximum daily 8 h mean) and O x were 22±11, 90±40, 25±5, 136±35 and 112±21 μg/m 3 in summer, respectively. During the Olympic Games, the mean concentration of SO 2 , PM 2.5 , NO 2 , O 3_8h max , and O x were 12.5±4, 56±28, 23±4, 114±29, 95±17 μg/m 3 in the region, respectively, and fell by 51.0%, 43.7%, 13%, 20.2%, and 18.9%, respectively, compared to the prophase mean before the Olympic Games. The concentration of atmospheric pollutants declined significantly and achieved the "Green Olympics" control goal of air quality. After the Olympic Games, SO 2 , PM 2.5 and NO x increased significantly as the temporary atmospheric pollution control measures were terminated.