Vertical distribution and transport characteristics of ozone pollution based on lidar observation network and data assimilation over the Pearl River Delta, China

Abstract

In recent years, China has made certain progresses regarding the monitoring of ozone (O3) pollution. However, a comprehensive understanding of the three-dimensional distribution and evolutionary characteristics of O3 is still relatively lacking. This study analyzed an O3 pollution episode in the Pearl River Delta during September to October 2019 using data from five O3 lidars and air pollution monitoring stations combined with the Gridpoint Statistical Interpolation data assimilation system. The model's performance in the vertical direction improved after assimilation, with the correlation coefficient of model simulations improving by 87 %, errors decreasing by 30 %, and simulation accuracy increasing by 29 %. Results showed that O3 pollution persisted for more than a week due to high temperatures and the influence of Typhoon Mita. However, after October 2, the concentration of O3 decreased under the combined effects of southerly winds and reduced traffic emissions during the National Day period. Besides, lidar observations indicate that residual O3 at night can disrupt its typical diurnal variation patterns. Moreover, O3 pollution occurred both at ground level and greater heights. Overall, O3 is primarily produced by photochemical reactions. Nevertheless, the O3 concentration was also affected by pollutant transport from northeast to southwest at a height of 0–3 km during the pollution period, with an average transport flux of 366 μg·m−2·s−1. Anomalously high nighttime O3 concentrations (>100 μg·m−3) were observed in both coastal and inland cities. Residual O3 could lead to persistent pollution the next day. The results clarify the vertical distribution and evolutionary characteristics of O3, which is crucial for devising more targeted pollution control strategies in the Pearl River Delta.