Environmental Chamber Studies of Voc Species in Architectural Coatings and Mobile Source Emissions

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 NO x levels of 25-30 ppb and at ambient surrogate ROG/NO x ratios representing maximum incremental reactivity (MIR) and NO x-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 …