The study applied 2008-2012 hourly mass concentrations of SO_2, NO_2 and PM_(10) and air pollution indexes (API) to discuss the temporal variation of urban air quality in Nanchong, a southwest city in China. The results showed that the total annual mean SO_2, NO_2 and PM_(10) concentrations during the 5 years were 0.045±0.004mg/m~3, 0.035±0.005mg/m~3, 0.061±0.001 mg/m~3, respectively. And the annual mean concentrations and API values presented decreasing tendency, which were less than the annual second-level air quality limit except for NO_2 (0.042mg/m~3) in 2008. In addition, the monthly mean values in spring and winter were higher than those in summer and fall, which the maximum appeared in December, January and February and the minimum appeared in June, July and August. The ratio of reaching standard presented increasing tendency, but PM_(10) and SO_2 were the main contribution to air pollution in Nanchong.
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