Uncertainty analysis of chamber-derived incremental reactivity estimates for n-butyl acetate and 2-butoxy ethanol

This study examines uncertainties in the calculated ozone-forming potentials of two oxygenated organic compounds for which environmental chamber data are available to test the chemical mechanisms used. For 2-butoxy ethanol, kinetic and product data are available for most reaction pathways, while for n-butyl acetate, only kinetic and environmental chamber data are available. The analysis accounts for uncertainties in the parameters of the compounds’ mechanisms that are adjusted to fit environmental chamber data, as well as in the parameters of the base SAPRC-97 chemical mechanism used to calculate the incremental reactivities. Uncertainties in the conditions of the chamber experiments are taken into account when deriving the uncertainty contributions of the parameters adjusted to fit chamber data. The results indicate that uncertainties in the reactivity estimates for 2-butoxy ethanol are lower than those estimated previously for many other emitted organic compounds, while those for n-butyl acetate are comparatively high. The parameters of the two compounds’ mechanisms that are derived from chamber experiments contribute at most about 7% of the uncertainty in their incremental reactivities. The availability of OH radical rate constant data is estimated to reduce the uncertainty in the relative maximum incremental reactivities (MIRs) for these compounds by 20–30%. Mechanistic and chamber data are estimated to reduce the uncertainty in the relative MIR of 2-butoxy ethanol by an additional 16%, but the available chamber data are estimated to reduce the uncertainty in the relative MIR of n-butyl acetate by only 3%. These results are based on subjective estimates of uncertainties in our ability to estimate mechanistic parameters and rate constants when no data are available.