Dependence of particle nucleation and growth on high-molecular-weight gas-phase products during ozonolysis of α-pinene

Measurements of products having mole fractions ranging from 10-14 to 10-11 were carried out with a chemical ionization mass spectrometer (the Cluster CIMS). Most products that were correlated with number concentrations of the smallest particles measured (10-20 nm) had molecular weights in the 430-560 amu range.

Those products are proposed to be likely responsible for the initial nuclei formation and the early growth of the freshly nucleated particles based on their high molecular weights and chemical identities, both of which suggest low-volatility compounds. Another group of oxidation products in the lower mass range of 140-380 amu was well correlated with particles larger than 20 nm. We postulate that those products contributed to the later growth of particles (i.e., larger than 20 nm in diameter).