Aerosol Particle Formation from Ozone-Terminal Olefin Reactions

Abstract

Gas phase reactions between ozone and two olefins, 1-hexene and 1-octene, were investigated for their aerosol formation. The reactions were studied in an atmosphere of 80% nitrogen and 20% oxygen (one atmosphere total pressure) in a glass tube 2.8 m long and 5 cm in diameter, with a steady flow at room temperature (296°K ± 2°). Aerosol formation was measured at various ozone and olefin concentrations. The overall rate constants for the production of particulate material were found to be 6.2 × 10⁻² and 12 × 10⁻² μg/m³-ppm²-sec for 1-hexene and 1-octene respectively. The estimated particle diameter ranged from 0.02 to 0.06 μm (1-hexene) and 0.04 to 0.08 μm (1-octene) with an approximate coagulation constant of 5 × 10 ⁻¹⁰ sec⁻¹ (nuclei/cc)⁻¹ for 1-hexene derived particles. Water and butyraldehyde, each separately introduced into the reaction, have significant effects suppressing the formation of particles. As part of the experiment, values of the second-order ozone-olefin gas phase reaction were determined to be 7.9 ± 0.40 × 10³ M⁻¹ for 1-hexene and 21 ± 0.3 × 10³ M⁻¹ sec⁻¹ for 1-octene. These rates basically agree with others reported in the literature, and establish continuity between the results for particle production and the gas phase chemistry studied by others.