Analysis of surface and vertical measurements of O3 and its chemical production in the NCP region, China

Ozone has become a major atmospheric pollutant in the North Central Plain (NCP) of China. Comprehensive measurements concerning the vertical profiles and photochemical formation mechanisms of typical O-3 pollution episode during August 8-13, 2018 were conducted in the NCP. A maximum hourly ozone concentration of 346 mu g/m(3) was observed on Aug 10, in which the surface O-3 photochemistry was under a strong VOC-limited regime, and the ratio of VOC to NOx ranged from 4:1 to 4:3, with ethylene, toluene, xylene, and propene providing large contributions to O-3 chemical production. The vertical measurements of O-3, NOx, and the planetary boundary layer (PBL) height suggested that there were three different layers of photochemical O-3 production from the surface to 1.1 km. The first layer was from the surface to 200 m, with high NO concentrations leading to a strong conversion between O-3 and NO2. The surface O-3 concentration was significantly lower than at 220 m during nighttime and early morning, with an average O-3 of approximately 60 mu g/m(3) and the maximum vertical gradient appearing in the early morning. Diurnal variations of NO2 and NO2 were significantly inversely correlated with O-3 and O-3. In the second vertical layer between 200 m and 1000 m the value of d [O-3]/dt ranged from 10 to 40 mu g/m(3)/h, and the maximum chemical production of O-3 occurred at 300 m. The third layer was located outside the PBL height, where O-3 precursors with short chemical lifetimes rapidly decreased, producing weak chemical O(3)production.