Temperature and stagnation effects on ozone sensitivity to NOx and VOC: an adjoint modeling study in central California

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 sensi-
tivity 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 meteoro-
logical 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 emis-
sion 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 un-
der 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, in-
creasing 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 loca-
tions 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.