A Dual-Perspective Analysis of Ozone Formation Sensitivity in the Yangtze River Delta: Satellite and Ground-Based Evidence

Abstract

Surface ozone (O3) pollution persists in the Yangtze River Delta (YRD) of China, with frequent exceedances despite stringent controls, driven by complex NOx-VOC interactions. Current monitoring struggles to accurately identify O3 formation regimes (VOC- vs. NOx-limited) at urban scales during daytime. By integrating TROPOMI satellite data with high-resolution ground-based joint observations, we reveal scale-dependent regime transitions: megacities (G1 cities, population > 5 million and GDP > 1 trillion CNY yr−1) exhibit narrow HCHO-to-NO2 ratio (FNR) transition ranges (1.54–2.86), and O3 pollution (≥160 μg/m−3) may occur under all regimes (VOC-limited, transitional, and NOx-limited). In contrast, smaller G2 cities show wider transition ranges (1.85–3.43), with O3 pollution occurring primarily under transitional and NOx-limited conditions. Observations from a typical G1 city demonstrate that VOC reductions effectively control O3 under VOC-limited regimes, while NOx mitigation alone is insufficient in NOx-limited environments due to persistently high VOC backgrounds. Our findings suggest city-specific strategies: G1 cities require adaptive co-control of VOCs and NOx to accommodate localized chemistry, whereas G2 cities benefit from targeted measures aligned with dominant sensitivity regimes. This study provides observational verification of environment-dependent O3 formation mechanisms, offering a methodological framework for precision air quality management in rapidly developing regions.