Spatiotemporal Dynamics of Nitrogen Dioxide and Ozone Interactions in Urban Atmospheres: A Multi-Site Observational Study

• • Inverse NO2-O3 correlation coefficients ranged from -0.72 to -0.85 across urban sites, indicating strong photochemical coupling; this suggests that NO2 reductions may initially increase O3 in VOC-limited areas, complicating control strategies. • • O3 peaks occurred 3-4 hours after NO2 minima, confirming photochemical production; this lag informs diurnal emission management and forecasting models. • • Generalized additive model explained 78% of O3 variability, with NO2 contributing 34% and temperature 22%; this quantifies the dominant drivers, enabling targeted mitigation. • • Weekend effect: 12% increase in O3 with reduced NO2 emissions, highlighting VOC-limited chemistry; this implies that NOx-only reductions may worsen O3, necessitating VOC co-control.