Comparisons of EPA Rollback, Empirical/Kinetic, and Physicochemical Oxidant Prediction Relationships in the San Francisco Bay Area

Abstract

This paper describes, compares and evaluates selected Oxidant Prediction Relationships {OPRs) in terms of projections of hydrocarbon emission reductions required for attainment of the former 0.08 ppm standard and the new 0.12 ppm standard in the San Francisco Bay Area in 1985. The OPRs analyzed are the LIRAQ physicochemical model, EPA’s Empirical Kinetic Modeling Approach (EKMA), linear and Appendix J rollback, and an empirical OPR based on local observations. LIRAQ simulations indicated that to achieve the 0.12 ppm ozone standard, 1985 hydrocarbon emissions must be reduced by 27% from projected levels. The equivalent reductions derived from simple linear rollback, linear rollback with 0.04 ppm background, and the local empirical OPR were 32%, 45% and 37%, respectively. The LIRAQ simulations also showed that reduction of both hydrocarbon and NOx emissions is less effective than reduction of hydrocarbons only. The attempt to apply EKMA failed because the Bay Area’s low hydrocarbon/NOx ratios and observed o...