The reaction kinetics of submicron oleic (9-octadecanoic (Z)-) acid aerosols with ozone was studied using a novel aerosol mass spectrometric technique. In the apparatus a flow of size-selected aerosols is introduced into a flow reactor where the particles are exposed to a known density of ozone for a controlled period of time. The aerosol flow is then directed into an aerosol mass spectrometer for particle size and composition analyses. Data from these studies were used to: (a) quantitatively model the size-dependent kinetics process, (b) determine the aerosol size change due to uptake of ozone, (c) assess reaction stoichiometry, and (d) obtain qualitative information about the volatility of the reaction products. The reactive uptake probability for ozone on oleic acid particles obtained from modeling is 1.6 (¿0.2) ¿ 10-3 with an upper limit for the reacto-diffusive length of ~10 nm. Atmospheric implications of the results are discussed.