Summertime ozone sensitivity to temperature in China: observational evidence and mechanistic attribution in urban and rural areas in the Yangtze River Delta region

Abstract

As climate change increases frequency and intensity of hot extremes, understanding how elevated temperatures influence surface ozone (O 3 ) across different chemical regimes is critical. We combine observations from summer 2022 in the Yangtze River Delta (YRD) with controlled United Kingdom Chemistry and Aerosols (UKCA) Box experiments for urban Shanghai and a lower-NO x , biogenically influenced Lishui regional environment. Observed daily-maximum O 3 increases with temperature at both sites, with a stronger response in Shanghai. Two-dimensional T -RH distributions show that O 3 rises with temperature and decreases with relative humidity (RH), implying that part of the temperature response is mediated by drying. Factorial box-model experiments separate the roles of temperature-driven shifts in chemical partitioning, diurnal thermal structure, temperature-dependent isoprene emissions, and humidity. In Shanghai, the increase in O 3 between 30 and 40 °C is dominated by BVOC-driven chemistry, with temperature-amplified isoprene emissions explaining most of the observed response. In Lishui, O 3 sensitivity is governed primarily by radical-NO x chemistry and thermal PAN-NO x cycling, with a much smaller role for BVOCs. Fixed RH scenarios substantially reduce the apparent contribution of “thermal chemistry”, highlighting humidity-dependent O x loss and HO x -NO x cycling as key modifiers of the climate penalty. Because the 0-D framework excludes transport and meteorological dynamics, the reported fractions isolate the local chemical and emission-driven component of the O 3 -temperature relationship. Within this scope, the results identify robust regime-specific mechanisms linking heat, humidity, precursor chemistry, and surface O 3 in the YRD and demonstrate the value of observation-constrained box models as a bridge to regional chemistry-climate simulations.