UNCERTAINTIES IN INCREMENTAL REACTIVITIES OF VOLATILE ORGANIC-COMPOUNDS

Uncertainties in the rate parameters of a gas-phase chemical mechanism have been propagated through simulations of urban ozone formation to estimate uncertainties in calculated incremental reactivities of selected organic compounds. Incremental reactivities were defined as the sensitivity of the predicted ozone concentration to the initial concentration of each organic compound in a mixture. Uncertainties (1 sigma) in the reactivities ranged across compounds from about 30% to about 70% of mean estimates. Uncertainties in the rate constants of the reactions NO + O-3; NO2, O-3, and HCHO photolysis; (OD)-D-1 + H2O; HNO3 formation; and PAN chemistry were found to be influential. For the reactivities of most compounds, rate constants of their primary oxidation steps were also influential. Because rate parameter uncertainties have directionally similar effects on the reactivities of most compounds, the significance of the uncertainties could be minimized by using reactivities in a relative sense.