Projecting ozone impact on crop yield in Taiwan under climate warming

Ozone is a primary air pollutant that impairs photosynthesis and reduces crop yields, an effect that received little attention in Taiwan, especially under the context of climate warming. This study predicted the impact of surface O₃ on cash crop yields, specifically in wheat, potatoes, and tomatoes, under 2 °C and 4 °C climate warming scenarios in Taiwan via high-resolution simulations. The simulated O₃ concentration (daytime mean) over Taiwan's croplands during the growing seasons was around 35-52 ppb, and it increased by 0.9 and 2.1 ppb under 2 °C and 4 °C warming for wheat and potatoes. In contrast, more minor changes of around 0.4 ppb were found for tomatoes. The O₃ concentrations were converted to AOT₄₀ (Accumulated Ozone exposure over a threshold of 40 ppb) and POD₃ (Phytotoxic Ozone Dose above a threshold of 3 nmol O₃ m^-2) metrics to estimate changes in relative yield (RY). The mean RY_POD3 (RY_AOT40) reductions over irrigated cropland for wheat, tomatoes, and potatoes under current climate and O₃-stress conditions are 27.5 % (19.1 %), 14.7 % (3.8 %), and 8.2 % (1.6 %), respectively. Under 2 °C warming, the additional reductions would be 2.7 % (1.8 %) for wheat, 4.1 % (0.3 %) for tomatoes, and 2.4 % (0.4 %) for potatoes; the values under 4 °C warming become 4.7 % (4.1 %) for wheat, 8.1 % (0.6 %) for tomatoes, and 5.2 % (0.8 %) for potatoes. The contribution of RY_POD3 reduction was separated into O₃-induced and climate-induced effects. The former dominated the additional yield reduction under a 2 °C warming climate, yet, the latter prevailed under 4 °C warming. Further analysis indicated that the temperature rise enhances ozone uptake flux; still, the amplified water vapor deficit and more incoming solar radiation can offset it and weakens the overall meteorological effect, especially from 2 °C to 4 °C warming conditions. Such effects demonstrated a nonlinear effect related to the co-dependence of the ozone uptake flux, which requires attention in agriculture policymaking.