FIRST-ORDER SENSITIVITY AND UNCERTAINTY ANALYSIS FOR A REGIONAL-SCALEGAS-PHASE CHEMICAL MECHANISM

First-order sensitivity and uncertainty analysis methods have been app lied to the RADM2 mechanism, the second generation gas-phase chemical mechanism included in the Regional Acid Deposition Model. The direct d ecoupled method (DDM) was used to evaluate the local sensitivity of pr oduct concentrations of O-3, HCHO, H2O2, PAN, and HNO3 to values of 15 7 rate constants and 126 stoichiometric coefficients. The sensitivity analysis results were combined with estimates of the uncertainty in ea ch parameter in the mechanism to produce a: local measure of its contr ibution to the uncertainty in the outputs. Several different sets of s imulation conditions were used, representing summertime surface condit ions for urban and nonurban areas. The analysis identified the most in fluential rate parameters to be those for PAN chemistry, formation of HNO3, and photolysis of HCHO, NO2, O-3, and the unknown product (DCB) of aromatics oxidation. Rate parameters for the conversion of NO to NO 2, such as O-3 + NO, HO2 + NO and organic radical + NO, and the produc t yields of organic peroxy radical (XYLP) in the reaction of XYL + HO (XYL represents xylene and more reactive aromatics) and DCB in the rea ction XYLP + NO are also relatively influential.