[Ozone Spatial-temporal Distribution and Trend over China Since 2013: Insight from Satellite and Surface Observation]

Satellite and surface observed O₃ concentrations were applied to analyze the spatial-temporal distribution and trends of O₃ over China. The satellite and surface observations agree well, revealing that the highest concentrations of O₃ are distributed in East China, and with a seasonal pattern of high in summer and low in winter. Records of the diurnal variation of O₃ over the four cities of interest (Beijing, Shanghai, Guangzhou, and Chengdu) reveal that O₃ peaked at 15:00-16:00 each day. Statistical analysis indicates that there is no significant difference in O₃ concentration between weekends and weekdays for the cities of Beijing, Guangzhou, and Chengdu. Surface O₃ over China increased dramatically from April 2013 to June 2018. The increase of the surface O₃ concentration from 2014 to 2017 is significant for Beijing, Shanghai, and Chengdu, and the rates of increase were 2.36, 3.3, and 3.6 μg·(m³·a)^-1, respectively. Analysis based on the daily max 8 h rolling mean O₃ concentration reveals that the percentage of days with O₃ concentration exceeding the national standard (160 μg·m^-3) in 2014-2017 were 17.2% for Beijing, 10.7% for Shanghai, 8.8% for Guangzhou, and 11.2% for Chengdu. O₃ pollution is most severe in Beijing where the highest O₃ concentration occurs, along with the largest number of days with daily max 8 h rolling O₃ concentration exceeding 160 μg·m^-3.