The influence of lightning activity on NO_x and O₃ in the Pearl River Delta region

Extremely high-temperature lightning generates NO_x by electrolyzing nitrogen and oxygen molecules, regulating ozone concentration. The Pearl River Delta (PRD) is located in the world's high-value area of lightning density, and lightning-generated NO_x (LNO_x) cannot be ignored. Using the flash data from Guangdong-Hong Kong-Macao Lightning Location System and multi-site atmospheric composition data, we estimate the NO_x variations in lightning activity and its impact on O₃ across the PRD region. The cloud-to-groud (CG) frequency from 2013 to 2021 shows a decreasing trend driven by urban regions. We observe that the lightning density is steadily decreasing from the south-central part of Guangzhou City to the surrounding area. A comparison of the different sites with lightning days and non-lightning days shows that a significant amount (13. 84-20. 47 %) of ground-level NO_x concentration at urban stations can be attributed to lightning NO_x emissions. A lower lightning frequency and low background concentration observed at suburban sites indicated a limited contribution of LNO_x. The average decrease in O₃ concentration at urban stations (15.92-25.06 %) was significantly higher than that at suburban stations (5.34-8.95 %) due to the influence of titration and lower actinic radiation. There was a greater fluctuation in NO_x and O₃ concentrations during the cases, and the surface NO_x concentration displayed the most significant responsiveness to LNO_x under direct lightning striking in the tall tower. This phenomenon has not been reported, however, it is consistent with the laboratory-based observations suggesting the amount of LNO increases with peak current. LNO_x significantly impacts air quality in the PRD during the high convective season. Further in situ and vertical distribution observations are necessary to explore the ground-level impact of LNO_x.