An experimental and modeling study was carried out to reduce uncertainties in atmospheric ozone impacts of architectural coatings VOCs. The focus of this project was Texanol® (isobutyrate monoesters of 2,2,4-trimethyl-1,3-pentanediol), which is widely used in water-based coatings, and various hydrocarbon solvents representative of those used in solvent-based coatings. The hydrocarbon “bin” reactivity assignments developed by the CARB for hydrocarbon solvents were evaluated using compositional data from 124 different solvents, and a new methodology was developed for deriving such assignments that can be used when reactivity scales are updated or modified. Progress was made towards developing a direct reactivity measurement method that does not require gas chromatographic analyses, but additional work is needed before data can be obtained for solvents of interest. Environmental chamber experiments were carried out to evaluate the abilities of mechanisms of Texanol® and six different types of hydrocarbon solvents to predict their atmospheric ozone impacts, and comparable experiments were carried out with m-xylene and n-octane for control and comparison purposes. Chamber data were also used to derive rate constants for the reactions of OH radials with the Texanol® isomers that are in excellent agreement with current estimates. The UCR EPA environmental chamber was employed, and the experiments were carried out at NOx levels of 25-30 ppb and at ROG/NOx ratios representing maximum incremental reactivity (MIR) and NOx-limited conditions. The current SAPRC-99 mechanism was found to simulate the results of the experiments with Texanol® and the primarily alkane petroleum distillate solvents reasonably well, though uncertainties exist because of problems with the model simulating results of the MIR base case experiments. The mechanism also simulated the effects of Aromatic 100 on O3 formation in the MIR experiments, but underpredicted the tendency for the aromatics to inhibit O3 in NOx -limited experiments and had other problems. The results of the experiments with the synthetic C10-C12 isoparaffinic mixture were not well simulated by the model, and suggest that current mechanisms may underpredict their atmospheric reactivities by 25-75% depending on the source of the discrepancy. Recommended needs for additional research are discussed.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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