Particle nucleation from the reaction of α-pinene and O3

Nucleation precursors from α-pinene+O3 reactions were investigated with a flow reactor combined with a Teflon bag reactor. Initial particle formation exponentially increased with the reacted amount of α-pinene with O3, and this, given certain assumptions, is consistent with classical nucleation theory. Initial reaction products indicated products such as cis-pinonaldehyde, cis-pinonic acid, cis-norpinonic acid, and pinalic-4-acid did not initiate particle self-nucleation because of their low concentrations compared to their theoretically estimated saturation concentrations. Although particle formation was observed on the time scale of the flow reactor (⩾0.4–6 s), cis-pinic and cis-norpinic acid were not detected as products, and hence are also not candidates for initiating self-nucleation. Thermally stabilized Criegee intermediates (SCI) were implicated in the nucleation process. Evidence for this comes from the observation of significant reductions in particle formation by scavenging SCIs with low-molecular-weight compounds. On a molecule reaction basis, nucleation was suppressed with SCI scavengers in the following order: water ≪acetaldehyde≈methanol