Abstract:
In order to explore the vertical distribution characteristics of warm season ozone pollution and its influencing factors, comprehensive long-term observations were conducted on ozone mass concentration and wind profiles within the atmospheric boundary layer up to 2 000 m above the coastal area of Qingdao from June to September 2023, by using differential absorption ozone lidar and coherent Doppler wind lidar. Possible pollution sources were revealed based on the vertical distribution of ozone transport flux. The research results show that: (1) The observation identified 24 pollution days and 98 clean days, with average O
3-8 h (daily maximum 8 h moving average of ozone mass concentration) of (183±24) and (118±30) μg/m
3, respectively. The ozone pollution processes were closely related to rising temperatures and were more likely to occur under conditions of intense solar radiation and lower relative humidity. (2) The vertical distribution of ozone was predominantly distributed below 1 000 m. On clean days, ozone mass concentration was relatively uniform, with minimal fluctuations in both daytime and nighttime at different altitudes. However, on pollution days, ozone mass concentration showed a unimodal diurnal variation at different altitudes, and the diurnal variation characteristics weakened as height increased. The vertical profiles of ozone mass concentration showed peaks during both daytime and nighttime on clean days, and during nighttime on pollution days. The peak concentrations were (115±3), (112±2) and (130±3)μg/m
3, respectively. These layered peaks were observed in the height range of 400 m to 650 m, and could be attributed to near-surface NO titration effects or the daytime high concentrations of ozone stored in the residual layer. However, the daytime ozone mass concentration profiles indicated a gradual decrease with increasing height on pollution days, suggesting that near-surface photochemical production was the primary source of ozone pollution. (3) Atmospheric conditions such as alternating northwest to southwest winds, low-level warm advection, and strong subsidence airflow were conducive to ozone and its precursors accumulation and ozone formation, leading to ozone pollution. On clean days, the lower atmosphere (from near the surface to 600 m) was predominantly influenced by clean maritime airflow, while on pollution days, it was originated from inland airflows. (4) From the early morning to the morning on the pollution days, ozone was transported from upwind areas in the west, southwest, or northwest. Ozone from higher altitudes was then mixed downward to the surface by downdrafts, where it combined with ozone generated by local precursors under meteorological conditions of high air temperatures and intense solar radiation, thereby exacerbating ozone pollution. Subsequently, the strong wind facilitated the transport of these elevated ozone to downwind areas in the afternoon. This study suggested that the prevention and control of ozone pollution should not only focus on precise control of local precursors, but also strengthen regional collaborative efforts to achieve continuous improvement of air quality.