EVALUATION OF ATMOSPHERIC IMPACTS OF
SELECTED COATINGS VOC EMISSIONS
Final Report to California Air Resources Board Contract No. 00-333
March 21, 2005
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.
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ENVIRONMENTAL CHAMBER STUDIES OF VOC
SPECIES IN ARCHITECTURAL COATINGS AND MOBILE SOURCE EMISSIONS
Final Report to South Coast Air Quality Management District Contract
No. 03468
July 5, 2005
Environmental chamber experiments were carried out to assess the atmospheric ozone and particle matter (PM) impacts of selected representative VOCs emitted from architectural coatings. The UCR EPA environmental chamber was employed for the ozone and PM impact experiments, and most consisted of incremental reactivity experiments carried out at NOx levels of 25-30 ppb and at ambient surrogate ROG/NOx ratios representing maximum incremental reactivity (MIR) and NOx-limited conditions. The compounds studied included the representative water-based coatings VOCs ethylene and propylene glycol, 2-(2-butoxyethoxy)-ethanol (DGBE), and benzyl alcohol. In addition, measurements of PM formation were made in experiments for these compounds and also in experiments with Texanol® (isobutyrate monoesters of 2,2,4-trimethyl-1,3-pentanediol), and several representative hydrocarbon solvents that were carried out for a separate project for the California Air Resources Board. Information was also obtained about PM background effects in the environmental chamber experiments.
The results of the chamber experiments were used to evaluate the predictions of the SAPRC-99 mechanism. The existing mechanism for DGBE was found to simulate the ozone reactivity data adequately, and a new mechanism for benzyl alcohol was developed that simulated the chamber data as well as mechanisms for other aromatics. The existing mechanisms for ethylene and propylene glycols were found to underpredict their ozone impacts by ~20% and 25-30% in some, but not all, experiments, but no scientifically acceptable basis was found to modify the mechanisms to improve these predictions. It is possible that that this is due to problems with the mechanisms for the aromatics present in the base ROG. The results of the experiments were also used to derive rate constants for the reactions of OH radicals with DGBE and benzyl alcohol relative to that for m-xylene, of 5.04 x 10-11 and 2.56 x 10-11, respectively. The rate constant for DGBE is in good agreement with the estimated value used by SAPRC-99, and that for benzyl alcohol is in good agreement with another measurement in the literature.
In terms of PM impacts in the incremental reactivity experiments, the relative ordering was found to be benzyl alcohol >> DGBE > petroleum distillates > a synthetic hydrocarbon solvent consisting mainly of branched alkanes " Texanol® > ethylene and propylene glycols. The benzyl alcohol was found to have a surprisingly high PM impact compared to other aromatics, and the glycols were found to actually reduce PM levels in the experiments, probably due to reducing rates of reactions of other VOCs present in the incremental reactivity experiment. No clear correlation between aromatic content and PM formation potential in the hydrocarbon solvents was seen. Background PM formation was observed in the chamber that will need to be characterized before these data can be used for PM model evaluation. Exploratory availability experiments were carried out to assess whether the presence of (NH4)2SO4 and NH4HSO4 seed aerosol at levels up to ~10 µg/m3 and humidity up to ~10% RH affected the gas-phase loss rates or ozone formation potentials of ethylene and propylene glycol, but effects were seen.
Experiments with updated ambient reactive organic gas (ROG) surrogate mixtures that represents current emissions from mobile and other sources were also planned for this project, but they could not be carried out because of a lack of time and resources to derive a target composition for a new ROG surrogate within the timescale needed for this project.