Temperature and stagnation effects on ozone sensitivity to NO x and VOC: an adjoint modeling study in central California

Abstract

Abstract. Extreme weather events like heatwaves and stagnation are increasing with climate change. While their effects on ozone levels have been extensively studied, how extreme weather alters O3-NOx-VOC sensitivity and optimal mitigation strategies is less explored. Here, we apply the CMAQ adjoint model over central California to quantify ozone sensitivity to spatiotemporally resolved precursor emissions under three meteorological scenarios (baseline, high-T, and stagnation) and three emission years (2000, 2012, and 2022). Results show that meteorology-induced changes in sensitivity are comparable in magnitude to those from decadal emission reductions. Higher temperature (+5 °C) amplifies ozone sensitivity to both NOx and VOC, with the largest relative increase in biogenic VOC sources. High-T conditions shift ozone chemistry toward NOx limitation under a VOC-limited emission scenario, but increase the relative importance of VOC control for a NOx-limited scenario. Stagnation consistently pushes ozone chemistry toward VOC limitation across emission scenarios, increasing VOC sensitivity by a factor of ∼ 3–4. Stagnation also spatially shifts influential source areas, especially for NOx, and temporally amplifies prior-day emission impacts due to enhanced pollutant carryover. As the study domain transitions to a NOx-limited regime over time, we identify a growing subset of “climate-resilient” source targets that remain impactful across meteorological scenarios, along with spatial convergence in optimal locations for NOx and VOC emission control. These findings underscore both the need and feasibility to consider meteorological extremes in the design of ozone mitigation strategies for a warming climate.