Studies of climate change increasingly recognize the diverse influences exerted by terpenes (Tp) in the atmosphere, including roles in particulates, ozone formation & their oxidizing potential. Measurements of key Tp suggest atmospheric concentrations ranging from low parts-per-trillion (ppt) to parts-per-billion (ppb), depending on location and compound. To accurately establish concentration trends, assess the role of Tp in atmospheric chemistry, & to relate measurement records from many laboratories and researchers, it is essential to have good calibration standards. The feasibility of preparing well-characterized, stable gas cylinder standards for terpenes at the ppb level is not yet well established. Several of the world s NMIs are researching the feasibility of developing primary & secondary reference gas standards at the ppb level for Tp. The U.S. NMI, the NIST, has prepared several ppb mixtures, in treated aluminum gas cylinders, containing Tp in dry nitrogen at nominal 5 ppb for stability studies. Overall 11 Tp were studied for stability. An initial gas mixture containing 9 Tp, 1 oxygenate & 6 aromatic compounds, including benzene as an internal standard, was prepared. Results for 4 of the 9 terpenes in this initial mixture indicate stability in these treated aluminum gas cylinders for over 6 months & project long term (years) stability. Interesting results were seen for -pinene which, when using a linear equation rate decline predicts that it will reach a zero concentration level at day 416. At the same time, increases in α-pinene, R-limonene and p-cymene were observed, including camphene, a Tp not prepared in the gas mixture, indicating a chemical transformation of -pinene to these species. Additional mixtures containing combination of either α-pinene, camphor, α-terpinene & benzene indicates a 2nd order quadratic rate declines for the α-pinene and α-terpinene, a linear rate decline for camphor & a 2nd order quadratic rate increase of camphene.
Citation: Analytical and Bioanalytical Chemistry
Pub Type: Journals
degradation, gas mixtures in aluminum cylinders, growth rate, internal standard, isomerization, parts per billion, terpenes (ppb)