The trend of surface ozone in Beijing from 2013 to 2019: Indications of the persisting strong atmospheric oxidation capacity

We report a continuous record of surface ozone (O₃) in urban Beijing, China, from 2013 to 2019. A linear fit to the 7-year record shows that the annual MDA8-O₃ (the maximum daily average of 8-h O₃ concentration) and annual average O₃ increased by 2.30 and 1.91 ppbv yr^-1 (p < 0.05), respectively. Both the MDA8-O₃ level and the number of exceeding days are increased, demonstrating the surface O₃ pollution in Beijing is increasingly serious. An overall decrease in annual surface NO₂ was observed at a rate of -1.21 ppbv yr^-1 (p < 0.01). The total oxidants (O_x, = NO₂ + O₃) had an upward trend during 2013-2019 at a rate of 0.70 ppbv h^-1 (p = 0.168). The increasing O₃ and O_x trends imply the atmospheric oxidation capacity is increasing in Beijing, even though the strict emission policies have been implemented. The periodical changes of surface O₃ in different time scales are studied. We found that the increases in O₃ are mainly at a high O₃ level with a threshold of 30 ppbv. The relative diurnal variability of surface O₃ is weakened, with a decrease in the diurnal amplitude variation. Both the extremely low and high 5% surface O₃ are increased, indicates an overall uplift of surface O₃. The weekday periodic trends showed an increment of weekend MDA8-O₃ (2.2 ppbv on average) and companies with a decrement of weekend NO₂ (1.5 ppbv on average). The weekend effect provides a chance to look insights into reducing O₃ exceeding days during summertime and proposes the need for emission abatements of volatile organic compounds to the mitigation of ozone pollution in Beijing.