The heterogeneous ozonolysis of sodium oleate aerosols in an aerosol flow tube is reported under different relative humidity (RH\%) conditions. Submicron sodium oleate particles were exposed to a known ozone concentration and the consumption of sodium oleate was monitored by infrared spectroscopy. When the experimental results are treated as a surface-mediated reaction (i.e., following a Langmuir-Hinshelwood type mechanism), the following parameters are obtained: at low RH\%, K-O3 = (3 +/- 1) x 10(-16) cm(3) molecule(-1) and k(max)(I) = (0.046 +/- 0.006) s(-1); at high RH\%, K-O3 = (6 +/- 2) x 10(-16) cm(3) molecule(-1) and k(max)(I) = (0.21 +/- 0.05) s(-1). From these pseudo-first-order coefficients, the reactive uptake coefficients for dry and aqueous sodium oleate aerosols are calculated as (1.5 - 0.5) x 10(-7) and (1.7 - 0.7) x 10(-6), respectively. Hydrated oleate aerosols display both an increase in the ozone trapping ability and an increase in the effective rate reaction at the droplet surface compared to dry aerosol surfaces. These observations may provide an explanation for some of the variability observed between lab studies of dry ozonolysis and real-world, atmospheric lifetimes of oleic acid-related species. (C) 2015 Wiley Periodicals, Inc.