[Characteristics of Ozone Background Concentration in Beijing from 2004 to 2015].

Based on the hourly O monitoring data from 2004 to 2015 of Beijing, a comprehensive discussion on the characteristics of O concentration at a background station Dingling in Beijing was conducted. The results showed that the annual concentration of O1h was increasing with a growth rate of 4.40 μg·m while the annual concentration of O8h was decreasing with annual average rates of -1.0 μg·m and -1.5 μg·m from May to October in 2004 and 2015. Over the past 3 years, number of O8h severe pollution days increased significantly and the situation of O pollution in Beijing became more serious. O concentration reached its peak in June in a year and its diurnal peak concentration occurred at about 15:00-18:00 at Dingling station which was 101-1.56 times larger than that in the urban center of Beijing. In different years, the ozone peak concentration at Dingling Station was 1h later than that in the urban center from May to October in diurnal variation and the difference of peak concentration was significantly reduced in recent years, which on the one hand may be related to regional ozone pollution, on the other hand may be related to the expansion of Beijing's urbanization.