A chamber study of alkyl nitrate production formed by terpene ozonolysis in the presence of NO and alkanes

Abstract

Organic nitrates are relatively long-lived species and have been shown to have a potential impact on atmospheric chemistry on local, regional, and even global scales. However, the significance of these compounds in the indoor environment remains to be seen. This work describes an impinger-based sampling and analysis technique for organic nitrate species, focusing on formation via terpene ozonolysis in the presence of nitric oxide (NO). Experiments were conducted in a Teflon film environmental chamber to measure the formation of alkyl nitrates produced from α-pinene ozonolysis in the presence of NO and alkanes using gas chromatography with an electron capture detector. For the different concentrations of NO and O₃ analyzed, the concentration ratio of [O₃]/[NO] around 1 was found to produce the highest organic nitrate concentration, with [O₃] = 100 ppb & [NO] = 105 ppb resulting in the most organic nitrate formation, roughly 5 ppb. The experiments on α-pinene ozonolysis in the presence of NO suggest that organic nitrates have the potential to form in indoor air between infiltrated ozone/NO and terpenes from household and consumer products.

Keywords: Indoor air; Occupational health; Organic nitrate; Sampling; Terpene.

Fig. 1.

Normalized GC-ECD chromatogram and peak areas of 2-ethylhexyl nitrate when captured using varying solvents. The peaks were normalized to the percent of solvent that evaporated during sampling to negate signal due to concentration of the solute.

Fig. 2.

Peak area versus concentration for isopropyl (A), isobutyl (B), and 2-ethylhexyl (C) nitrates added to ethyl acetate (spike) or injected into Teflon chambers then recovered by pulling through ethyl acetate impingers (chamber). Error bars represent the standard deviation of triplicate experiments.

Fig. 3.

Reaction scheme showing the formation of cyclohexyl nitrate initiated by α-pinene ozonolysis.

Fig. 4.

GC-ECD chromatogram for the production of cyclohexyl nitrate when ozone is added to the chamber containing α-pinene, cyclohexane, and NO (red). Controls (blue, black, green) confirm that all species are involved in the formation mechanism. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 5.

Plot of cyclohexyl nitrate peak area versus [NO] and [O₃] added to the chamber. Each vertex is the mean of triplicate experiments. Yield was determined by generating a calibration curve for synthesized cyclohexyl nitrate.

Fig. 6.

Plot of summed (A) pentyl nitrate peak areas and (B) hexyl nitrate peak areas versus [NO] and [O₃] added to the chamber. Each vertex is the mean of triplicate experiments.