Stable carbon isotope composition of secondary organic aerosol from β-pinene oxidation

Abstract

A chamber study was carried out to investigate the stable carbon isotopic composition (δ 13 C) of secondary organic aerosol (SOA) formed from ozonolysis of β-pinene. β-Pinene (600 ppb) with a known δ 13 C value (-30. 1‰) and 500 ppb ozone were injected into the chamber in the absence of light and the resulting SOA was collected on preheated quartz fiber filters. Furthermore, δ 13 C values of the gas-phase β-pinene and one of its oxidation products, nopinone, were measured using a gas chromatograph coupled to an isotope ratio mass spectrometer (GC-IRMS). β-Pinene was progressively enriched with the heavy carbon isotope due to the kinetic isotope effect (KIE). The KIE of the reaction of β-pinene with ozone was measured to be 1.0026 ( O 3 ε 2.6 ± 1.5‰). The δ 13 C value of total secondary organic aerosol was very similar to that of its precursor (average = -29.6 ± 0.2‰) independent of experiment time. Nopinone, one of the major oxidation products of β-pinene, was found in both the gas and aerosol phases. The gas-phase nopinone was heavier than the initial β-pinene by 1.3‰ but lighter than the corresponding aerosol-phase nopinone. On average, the gas-phase nopinone was lighter by 2.3‰ than the corresponding aerosol-phase nopinone. The second product found in the SOA was detected as acetone, but it desorbed from the filter at a higher temperature than nopinone, which indicates that it is a pyrolysis product. The acetone showed a much lower δ 13 C (-36.6‰) compared to the initial β-pinene δ 13 C. Copyright 2009 by the American Geophysical Union.