GLOBAL UNCERTAINTY ANALYSIS OF A REGIONAL-SCALE GAS-PHASE CHEMICAL MECHANISM

A global uncertainty analysis of the Regional Acid Deposition Model ve rsion 2 chemical mechanism was conducted to estimate the effect of unc ertainties in rate parameters and product yields on predicted concentr ations of ozone and other secondary pollutants. Uncertainties were als o estimated for changes in ozone due to 25% reductions in reactive org anic gases (ROG), nitrogen oxides (NOx) or both. The analyses were per formed for single-day box model simulations of summertime smog episode s, with uncertainties propagated using a Latin hypercube sampling sche me. The resulting uncertainties in peak ozone concentrations range fro m about 20 to 50% (+/- 1 sigma relative to the mean). Uncertainties in predicted concentrations range from 15 to 30% for HNO3, 20 to 30% for HCHO, and 40 to 70% for peroxyacetyl nitrate (PAN). Except with very low concentrations, uncertainties in H2O2 range from 30 to 45%. For th e cases studied the choice between ROG or NOx reductions as most effec tive for lowering ozone concentrations is insensitive to uncertainties in chemical parameters. Product concentrations are most strongly affe cted by uncertainties in rate parameters for PAN chemistry, HNO, forma tion, aromatics oxidation, the reaction of HO2 + NO, and photolysis of HCHO, NO2, and O-3, and uncertainties in peroxy radical yields from a romatics and olefins oxidation.