Uses and limitations of modeling in analyzing and designing O3 strategies

Abstract

A sufficient historical record in grid-based O3 modeling now exists to permit assessment of its role and limitations in policy analysis. In this presentation, several topics are examined: past experience in model evaluation and use, the present status of modeling, the value of modeling in policy analysis, and key issues and future needs. First, the role of grid-based O3 modeling in policy analysis was assessed through a case study of nearly 10 years of model applications in the South Coast (Los Angeles) Air Basin. Changes in quality of performance and in degree of acceptance of grid-based models (in policy analysis) with time were analyzed and compared. Degree of acceptance appears to depend on a variety of factors, including level of understanding and familiarity, perception of need, and relative degree of acceptability, as compared with other available models. Improvements in quality of performance with time were limited (and, in any event, knowledge of such changes were not available), and thus this factor seems to have had little or no role in influencing model acceptance. Second, the current state of modeling, in terms of both science and art, is appraised, considering the state of knowledge, availability of data bases, adequacy of performance evaluation procedures, and quality of predictive performance. Significant deficiencies have existed in knowledge and treatment of key governing processes in models. Until recently, data bases suitable for use in evaluating model performance were unavailable. Quality of performance has not been sufficiently good to confer confidence in models' use in a regulatory environment. Evaluative testing did not provide sufficiently for ‘stressing’ models. For many, but not all of these issues, attention is now being, or soon will be, given to alleviating concerns. Third, the role and value of modeling in policy analysis is discussed. Attention is given to the role of the modeling expert in the policy forum, as compared with the model itself, and with the consideration of modeling as a longer term process rather than as a direct or short term means of generating ‘answers’. Finally, key concerns and future needs are delineated, and some unsolved problems are discussed.