Exploring the High Summertime Surface Ozone-Temperature Sensitivity in China

Ozone-temperature sensitivity measures the increase in ozone concentration per Kelvin rise in temperature, serving as a critical metric for assessing ozone responses to climate warming. Here, from extensive observations across the Northern Hemisphere, we show that China exhibits a remarkably higher present-day (2017-2024) summertime surface ozone-temperature sensitivity (mΔO3-ΔTmax; 3.7 ppbv K-1) compared to the US (1.6 ppbv K-1) and Europe (1.8 ppbv K-1), with extremely high values reaching 8-10 ppbv K-1 at the site level. GEOS-Chem model simulations with improved accuracy in reproducing observed mΔO3-ΔTmax attribute this elevated sensitivity predominantly to temperature-indirect effects (66%), comprising comparable contributions from temperature-associated changes in radiation (44%) and transport patterns (51%). These indirect effects dominate the spatial and interannual variability of mΔO3-ΔTmax in China. Direct temperature effects on emissions, chemistry, and deposition account for the remaining 34%. Global models project that stringent emission reductions will decrease China's future mΔO3-ΔTmax to levels comparable to those of the US and Europe, highlighting emission levels as the primary determinant of the magnitude of ozone-temperature sensitivity. These findings emphasize that sustained emission controls are crucial for mitigating the risks associated with compound heat and ozone pollution.