Ozone formation in California's San Joaquin Valley: A critical assessment of modeling and data needs

Data from the 1990 San Joaquin Valley Air Quality Study/Atmospheric Utility Signatures, Predictions, and Experiments (SJVAQS/AUSPEX) field program in California's San Joaquin Valley (SJV) suggest that both urban and rural are as would have difficulty meeting an 8-hr average O-3 standard of 80 ppb. A conceptual model of O-3 formation and accumulation in the SJV is formulated based on the chemical, meteorological, and tracer data from SJVAQS/AUSPEX. Two major phenomena appear to lead to high O-3 concentrations in the SJV: (1) transport of O-3 and precursors from upwind areas (primarily the San Fr ancisco Bay Area, but also the Sacramento Valley) into the SJV, affecting t he northern part of the valley, and (2) emissions of precursors, mixing, tr ansport (including lon,orange transport), and atmospheric reactions within the SJV responsible for regional and urban-scale (e.g., downwind of Fresno and Bakersfield) distributions of O-3. Using this conceptual model, we then conduct a critical evaluation of the meteorological model and air quality model. Areas of model improvements and data needed to understand and proper ly simulate O-3 formation in the SJV are highlighted.