Role of meteorological processes in ozone responses to emission controls in California's San Joaquin Valley

[1] We conducted a first-order sensitivity analysis to investigate ozone responses to precursor emissions and source contributions (local versus upwind) for California's San Joaquin Valley (SJV) under four distinct meteorology conditions of summer 2000 using a three-dimensional photochemical transport model. Ozone-limiting reagents, nitrogen oxides (NO_x), or anthropogenic volatile organic compounds (VOCs) (AVOCs) and their transition regime were determined from ozone sensitivity coefficients and delineated spatially at high-ozone locations in the SJV. In general, AVOC-limited areas were located near urban centers, while NO_x-limited areas were located farther downwind. However, the spatial extent of AVOC-limited areas varied with meteorology. Meteorological dependence of predominant ozone-limiting precursors was found to vary significantly among different subregions within the SJV. Specifically, weaker dependences were identified for regions of the southern SJV located farther away from emission sources, where ozone chemistry was mostly limited by NO_x for the episodes considered. Stronger dependences were identified for the central and northern SJV, where ozone chemistry can be limited by NO_x or AVOC depending on meteorology. Source contributions to ozone sensitivities in the SJV were also investigated. Local sources were important for the eastern side of the central SJV, while upwind sources were also important (from ~40% to more than 50% of the total ozone sensitivities) for the western side of the valley, except for the most stagnant episode. Different contributing source regions were identified for the same VOC-limited areas in the northern SJV, and these depended on the flow characteristics. The predominant ozone-limiting reagent was found to exhibit less dependence on meteorology in the central and southern SJV as the baseline NO_x emissions were reduced, ultimately causing ozone formation to be limited by NO_x. In contrast, the VOC-limited areas in the northern SJV continued to be influenced by meteorology for two of the episodes.