Characteristics and Meteorological Mechanisms of Typical Nocturnal Ozone Increase Events in Suizhou, China

Abstract

In recent years, ozone pollution has become increasingly prominent in China. Surface ozone not only rises during the daytime but also exhibits secondary increases at night, defined as nighttime ozone increase events (NOIs). Using atmospheric pollutant concentration data from 2015 to 2023, this study analyzes the characteristics of NOIs in Suizhou, including their frequency, intensity, and nocturnal and daytime peak concentrations. The WRF-Chem model is also employed to simulate the event with the maximum intensity. The results show that a total of 614 NOIs occurred in Suizhou, accounting for 18.7% of the total observation period. The maximum intensity of these events reached 57 μg/(m³·h). In 12.2% of the NOIs, the nocturnal ozone peak (NOP) exceeded the previous daytime maximum (PDM), indicating that NOIs in Suizhou cannot be ignored. The simulation results indicate that large-scale subsidence transports ozone-rich air from the upper layers downward, while horizontal advection carries high-concentration ozone from northeastern Hubei Province to Suizhou. Furthermore, the drag effect of precipitation particles and turbulent disturbances following the initiation of nighttime convection further bring residual layer ozone to the surface. Collectively, these processes lead to the increase in nocturnal surface ozone concentrations.