Effect of alternative boundary conditions on predicted ozone control strategy performance: A case study in the Los Angeles area

The purpose of this paper is to illuminate the importance of assumptions made regarding boundary and initial conditions on the predicted performance of regional ozone control strategies. A computationally efficient approach to depicting the response of an air basin to emission controls is developed. The problem of ozone isopleth generation is addressed using a large Eulerian grid-based photochemical airshed model that is distributed over a grid system of 64 different ROG and NOx control combination points that were run simultaneously on a parallel computer. This method is used for the Los Angeles area to examine the effect on predicted ozone concentrations of alternative assumptions about how boundary conditions at the edge of the air basin will change as a result of changed recirculation of pollutants from within the airshed plus emission decreases upwind. We show that an accurate forecast of the effect of future emission control programs on pollutant inflows across the boundaries of the Los Angeles modeling region is absolutely critical to selection of a successful ozone control strategy for the Los Angeles area.