Impact of Southern California anthropogenic emissions on ozone pollution in the mountain states: Model analysis and observational evidence from space

We identified two to six major transport events from SoCal to different subregions in the mountain states, with transport times of 0-2 days indicated by trajectories, time-lag correlations, and forward/adjoint sensitivities. Based on forward sensitivity analysis, the contributions from SoCal anthropogenic emissions to the monthly mean daily maximum 8 h average (MDA8) surface O₃ in the mountain states decrease with distance from SoCal, and they range from 0.6) to strong (>0.8) positive correlations with the modeled total surface MDA8 O₃.

For the most strongly affected states of Arizona and New Mexico, these contributions have median values of ∼3, ∼2, ∼5, and ∼15 ppbv when the total surface MDA8 O₃: exceeded thresholds of 60, 65, 70, and 75 ppbv, respectively. Surface MDA8 Ò ;values in SoCal show strong nonlinear responses to varied magnitudes of perturbation (e.g., ±50% and 100%) in SoCal anthropogenic emissions and weak nonlinear responses in the mountain states.