Determination of the stable carbon isotopic compositions of 2-methyltetrols in ambient aerosols from the Changbai Mountains.

Isoprene is one of the most important non-methane hydrocarbons (NMHCs) in the troposphere: it is a significant precursor of O(3) and it affects the oxidative state of the atmosphere. The diastereoisomeric 2-methyltetrols, 2-methylthreitol and 2-methylerythritol, are marker compounds of the photooxidation products of atmospheric isoprene. In order to obtain valuable information on the delta(13)C value of isoprene in the atmosphere, the stable carbon isotopic compositions of the 2-methyltetrols in ambient aerosols were investigated. The 2-methyltetrols were extracted from filter samples and derivatized with methylboronic acid, and the delta(13)C values of the methylboronate derivatives were determined by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). The delta(13)C values of the 2-methyltetrols were then calculated through a simple mass balance equation between the 2-methyltetrols, methylboronic acid and the methylboronates. The delta(13)C values of the 2-methyltetrols in aerosol samples collected at the Changbai Mountain Nature Reserves in eastern China were found to be -24.66 +/- 0.90 per thousand and -24.53 +/- 1.08 per thousand for 2-methylerythritol and 2-methylthreitol, respectively. Based on the measured isotopic composition of the 2-methyltetrols, the average delta(13)C value of atmospheric isoprene is inferred to be close to or slightly heavier than -24.66 per thousand at the collection site during the sampling period.