Evolution of boundary layer ozone in Shijiazhuang, a suburban site on the North China Plain

The structure of the boundary layer affects the evolution of ozone (O₃), and research into this structure will provide important insights for understanding photochemical pollution. In this study, we conducted a one-month observation (from June 15 to July 14, 2016) of the boundary layer meteorological factors as well as O₃ and its precursors in Luancheng County, Shijiazhuang (37°53'N, 114°38'E). Our research showed that photochemical pollution in Shijiazhuang is serious, and the mean hourly maximum and mean 8-hr maximum O₃ concentrations are 97.9 ± 26.1 and 84.4 ± 22.4 ppbV, respectively. Meteorological factors play a significant role in the formation of O₃. High temperatures and southeasterly winds lead to elevated O₃ values, and at moderate relative humidity (40%-50%) and medium boundary layer heights (1200-1500 m), O₃ production sensitivity occurred in the transitional region between volatile organic compounds (VOC) and nitrogen oxides (NO_x) limitations, and the O₃ concentration was the highest. The vertical profiles of O₃ were also measured by a tethered balloon. The results showed that a large amount of O₃ was stored in the residual layer, and the concentration was positively correlated with the O₃ concentration measured the previous day. During the daytime of the following day, the contribution of O₃ stored in the residual layer to the boundary layer reached 27% ± 7% on average.