Reactive and nonreactive ozone uptake during aging of oleic acid particles

Abstract

The ozonolysis of submicrometer (150 nm) oleic acid (OL) particles in an aerosol flow tube has been studied for a wide range of initial ozone concentrations from 25 ppb to 1100 ppb. Both reactants were monitored, as well as the four main reaction products (nonanal, azelaic acid, nonanoic acid, and 9-oxononanoic), by gas chromatography-mass spectrometer, high resolution-time of flight-aerosol mass spectrometer, proton transfer reaction-time of flight-mass spectrometer, and ozone analyzer. The values for the initial uptake coefficients derived from each reactant decay are in the same range: γO3-0 = (1.5 ± 0.1) × 10-3 and γOL-0 = (1.0 ± 0.2) × 10-3. The ozone uptake coefficient is highly decreased when particles are in an advanced oxidized state (γO3-∞ = 5 × 10-5). Concerning reaction products, nonanal was mainly observed in the gas-phase (∼80%) with a carbon yield of ∼29%. Nonanoic, azelaic, and 9-oxonanonoic acids have been quantified in the condensed phase with carbon yields of respectively 6.6%, 5.3%, and 31.4%. The changes in chemical composition induce a slight rise in particle density, whereas the aerodynamic particle diameter increases by 10%. The initial molar quantities of ozone and OL were chosen to obtain different initial stoichiometries in order to explore conditions where either of them is the limiting reactant. Drastic changes in reactivity were observed as a function of the initial stoichiometry. In conditions where OL was the initial limiting reactant, up to a total of four molecules of O3 were lost from the gas phase, whereas only one OL molecule was consumed.