Temporal Characteristics of Ozone (O(3)) in the Representative City of the Yangtze River Delta: Explanatory Factors and Sensitivity Analysis

Ozone (O(3)) has attracted considerable attention due to its harmful effects on the ecosystem and human health. The Yangtze River Delta (YRD), China in particular has experienced severe O(3) pollution in recent years. Here, we conducted a long-term observation of O(3) in YRD to reveal its characteristics. The O(3) concentration in autumn was the highest at 72.76 ppb due to photochemical contribution and local convection patterns, with its lowest value of 2.40 ppb in winter. O(3) exhibited strong diurnal variations, showing the highest values in the early afternoon (15:00–16:00) and the minimum in 07:00–08:00, specifically, peroxyacetyl nitrate (PAN) showed similar variations to O(3) but PAN peak usually occurred 1 h earlier than that of O(3) due to PAN photolysis. A generalized additive model indicated that the key factors to O(3) formation were NO(2), PAN, and temperature. It was found that a certain temperature rise promoted O(3) formation, whereas temperatures above 27 °C inhibited O(3) formation. An observation-based model showed O(3) formation was VOCs-limited in spring and winter, was NO(x)-limited in summer, and even controlled by both VOCs and NO(x) in autumn. Thus, prevention and control strategies for O(3) in the YRD are strongly recommended to be variable for each season based on various formation mechanisms.