Impacts of Intensified Heatwaves on Escalation of Ozone and Reactive Nitrogen in Summer

High Resolution Image Download MS PowerPoint Slide Global warming has intensified the frequency and severity of heatwave events (HWs); however, the research on the interaction between O 3 and reactive nitrogen during HWs is far from sufficient. In this study, three types covering nine HWs events were identified during summer 2023 (June–August) in Beijing, including daytime HWs (DHWs, 4 days), nighttime HWs (NHWs, 8 nights), and compound HWs (CHWs, 27 days). Twenty-eight days of O 3 pollution (OP) occurred during the whole summer, among which 64% (18 out of 28) appeared during HWs. HWs elevated O 3 concentrations by 27.3% comparing to non-HWs, while CHWs significantly amplified diurnal O 3 fluctuations accompanied by the accumulation of reactive nitrogen (NOx, NOz, and NOy), indicting a stronger tendency toward O 3 -reactive nitrogen combined pollution. During HWs, NOx/NOy ratios were reduced, and secondary oxidized nitrogen NOz levels were elevated, which accelerated photochemical O 3 production and promoted VOC-driven chain reactions, thereby intensifying and prolonging O 3 pollution. O 3 suppression was observed at temperatures of ∼38 °C, indicating a nonlinear and complex influence of HWs on the O 3 formation. This work elucidates synergistic O 3 -reactive nitrogen transformation mechanisms under extreme HWs, providing a scientific foundation for refined regional pollution modeling and precision mitigation strategies.