USE OF SENSITIVITY ANALYSIS TO COMPARE CHEMICAL MECHANISMS FOR AIR-QUALITY MODELING

The LCC and CB4 mechanisms have been compared through a detailed sensitivity analysis. The formal method used provides an efficient means of comparing the influence of initial concentrations and reaction rate constants across mechanisms. The analysis identified discrepancies between the CB4 and LCC mechanisms that were overlooked in less formal tests. For the conditions studied, which approximate those of a smog chamber, the mechanisms generally show close agreement in predicted ozone concentrations, with larger differences for hydrogen peroxide and formaldehyde. The mechanisms differ in the sensitivity of peak O3, H2O2, and HCHO concentrations to the initial concentrations of key classes of organic compounds. These differences have important implications for use of the mechanisms in developing reactivity scales. Revisions to the CB4 mechanism that have been recommended based on recent studies of peroxy acetyl radical + NO and NO2 reaction rates are shown to be significant.